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Article

BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1) Composites Synthesized by Thermal Decomposition: Magnetic, Dielectric and Ferroelectric Properties

by
Marija Šuljagić
1,
Ivan Petronijević
2,
Miljana M. Mirković
3,
Aleksandar Kremenović
4,
Adis Džunuzović
5,
Vladimir B. Pavlović
6,
Aleksandra Kalezić-Glišović
7 and
Ljubica Andjelković
1,*
1
Department of Chemistry, University of Belgrade-Institute of Chemistry, Technology and Metallurgy, Njegoševa 12, 11000 Belgrade, Serbia
2
Faculty of Physics, University of Belgrade, Studentski Trg 12-16, 11000 Belgrade, Serbia
3
Department of Materials, “Vinča” Institute of Nuclear Sciences—National Institute of the Republic of Serbia, University of Belgrade, 11000 Belgrade, Serbia
4
Faculty of Mining and Geology, University of Belgrade, Djušina 7, 11000 Belgrade, Serbia
5
Institute for Multidisciplinary Research, University of Belgrade, Volgina 15, 11000 Belgrade, Serbia
6
Faculty of Agriculture, University of Belgrade, Nemanjina 6, Zemun, 11000 Belgrade, Serbia
7
Section for Amorphous Materials, Joint Laboratory for Advanced Materials of SASA, Faculty of Technical Sciences Čačak, University of Kragujevac, Svetog Save 65, 32000 Čačak, Serbia
*
Author to whom correspondence should be addressed.
Inorganics 2023, 11(2), 51; https://doi.org/10.3390/inorganics11020051
Submission received: 22 December 2022 / Revised: 13 January 2023 / Accepted: 16 January 2023 / Published: 19 January 2023
(This article belongs to the Section Inorganic Materials)

Abstract

:
To investigate the influence of spinel structure and sintering temperature on the functional properties of BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1), NiFe2O4, ZnFe2O4, and Ni0.5Zn0.5Fe2O4 were in situ prepared by thermal decomposition onto BaTiO3 surface from acetylacetonate precursors. As-prepared powders were additionally sintered at 1150 °C and 1300 °C. X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) coupled with electron dispersive spectroscopy (EDS) were used for the detailed examination of phase composition and morphology. The magnetic, dielectric, and ferroelectric properties were investigated. The optimal phase composition in the BaTiO3/NiFe2O4 composite, sintered at 1150 °C, resulted in a wide frequency range stability. Additionally, particular phase composition indicates favorable properties such as low conductivity and ideal-like hysteresis loop behavior. The favorable properties of BaTiO3/NiFe2O4 make this particular composite an ideal material choice for further studies on applications of multi-ferroic devices.

1. Introduction

In the last century, a sporadic interest in multiferroism was strongly influenced by a scarcity of materials [1,2]. The discovery of extreme electric polarization behavior in BiFeO3 and manganite multiferroic derivatives have accelerated research on this topic in the past two decades [3,4]. In the past few years, researchers have begun performing in-depth studies on magnetoelectric multiferroics. which are materials that display ferromagnetism and ferroelectricity simultaneously [5,6,7,8,9]. The perovskite compounds are one of the most promising types of magnetoelectric multiferroics [10,11,12,13,14]. The advantages of these novel materials can support the development of advanced devices and technologies [15,16,17,18,19,20].
There are only a few known multiferroic materials that combine the mutually exclusive functionalities of ferromagnetism and ferroelectricity in the same phase, specifically at approximately room temperature [16]. To overcome the rareness and shortcomings of single-phase magnetoelectrics, the scientific community has been focused on the development of advanced multifunctional composite materials. More specifically, the magnetoelectric coupling is a consequence of the strain induced on the interface between two different phases [21,22,23,24,25,26,27]. Such heterostructured materials can satisfy technological requirements by varying the microstructure of their constituents, their volume fraction, and/or the phase composition [28,29].
Barium titanate (BaTiO3) is a well-known compound used to develop magnetoelectric multiferroic materials. This is due to its unique dielectric properties in the tetragonal phase with the P4mm space group [30,31,32,33]. In order to design novel multiferroic composites based on barium titanate, ferrites are one of the ideal candidates due to their attractive magnetic properties [25,30,31,33,34,35,36,37,38]. Sintering is a required process for synthesis which primarily assures better mechanical coupling between ferrite and ferroelectric grains, while also promoting more pronounced magnetoelectric signals [39]. However, high sintering temperatures may lead to the formation of Fe2+ ions in such composites, which can cause interphase reactions and decrease electric resistivity, thus lowering the magnetoelectric response [40].
Among many spinel oxides, nickel ferrite (NiFe2O4) with an inverse spinel structure and soft magnetic nature, zinc ferrite (ZnFe2O4) with ferrimagnetic behavior in the nanometric range, alongside with mixed nickel zinc ferrites, stand out because their coercivity, electrical conductivity, and saturation magnetization can be easily tuned to address the competing demands for specific multiferroic applications [35,41,42].
Although the increase in spinel content negatively affects magnetoelectric response [40], careful selection of ferrite chemical composition, as well as an attentive choice of synthesis protocol may serve to overcome such negative influence [43,44,45]. Many different methods were developed for the synthesis of nanocrystalline nickel- and zinc ferrites with tailored characteristics [46,47,48,49,50,51]. The thermal decomposition of coordination compounds with simple organic ligands emerged as a method of choice due to the low reaction temperatures [52,53,54,55,56,57,58]. Metal carbonyls, metal carboxylates, and metal acetylacetonates were recognized as precursors to fabricate nanostructured magnetic oxides with uniform and narrow size distribution of nanoparticles, due to their high purity and cheap production [59,60,61,62,63,64,65].
This paper addresses a simple route to prepare a series of a composite of BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1) via the thermal decomposition of acetylacetonate complex precursors onto BaTiO3 surface and processing of obtained structures into dense ceramics. The effect of structural properties and phase composition, as well as two sintering schedules on dielectric and ferroelectric properties of synthesized ceramic composites, was studied and explained in detail.

2. Results and Discussion

The XRPD patterns for as-prepared and sintered titanate/ferrite structures are shown in Figure 1. With the increase in sintering temperature, better crystallinity was obtained, irrespective of the investigated powder. Furthermore, peaks intensity belonging to barioferrite-like phases indicated the more intensive reaction between spinel and BaTiO3 at 1300 °C. The phase composition for each investigated powder is given in Table 1. The presence of spinel and tetragonal BaTiO3 phases can be clearly seen for as-prepared samples. The zinc oxide (ZnO) phase is also evident in the case of BaTiO3/ZnFe2O4 while for the BaTiO3/Ni0.5Zn0.5Fe2O4, barioferrite-like phase was formed during the thermal decomposition process. In the case of sintered samples, different barioferrite-like phases were formed. However, spinel and tetragonal BaTiO3 phases remain unchanged. The transformation of BaTiO3 from P4mm to P4/mmm space group was observed at 1300 °C in all studied cases.
The SEM micrographs for as-prepared powders confirmed the presence of two types of particles, different in size and shape, Figure 2. The particles which belong to the BaTiO3 are bigger (0.5–1 μm) in comparison to ferrite particles that are in the sub-100 nm range. It was observed that ferrite particles formed agglomerates due to the size-driven surface activity [66,67]. The EDS maps of these samples confirmed the non-uniform distribution of barium-titanate and ferrite phases. The EDS layered images suggested that the best ferrite distribution over the titanate surface was achieved in the case of the as-prepared BaTiO3/NiFe2O4 composite, Figure 2. For the BaTiO3/ZnFe2O4 and BaTiO3/Ni0.5Zn0.5Fe2O4 powders clear separation of the Zn-rich phases was observed, Figure 2. These results are following XRPD analyses which showed the presence of a zinc oxide phase in the case of BaTiO3/ZnFe2O4 (Table 1). Furthermore, the lowest amount of the ferrite phase in the case of BaTiO3/ZnFe2O4, observed by XRPD (<30%, Table 2), indicates the sparse distribution of ZnFe2O4 over the BaTiO3 surface.
The SEM micrographs obtained for the samples sintered at 1150 °C revealed that this temperature was not enough to reach the final sintering stage, Figure 3. Most of the particles preserved their initial shape, followed by porosity that is typical for the intermediate sintering stages. EDS mapping of these samples showed the presence of the BaTiO3 cores covered with much smaller ferrite particles forming imperfect shells. However, localized ferrite phases, especially in the cases of BaTiO3/ZnFe2O4 and BaTiO3/Ni0.5Zn0.5Fe2O4 were noticed. Moreover and regarding BaTiO3/Ni0.5Zn0.5Fe2O4, besides ferrite and barioferrite phases, the occurrence of mixed nickel zinc oxide has been observed, corroborating phase analysis results.
The increase in temperature up to 1300 °C led to the occurrence of high-density regions, although some level of porosity was still present, Figure 4. EDS mapping confirmed that ferrite phases were uniformly covered the surface of BaTiO3. For the BaTiO3/ZnFe2O4 and BaTiO3/Ni0.5Zn0.5Fe2O4 samples, besides core/shell structures the formation of localized Zn-rich phases has been observed.
It should be noticed that the formation of core/shell structures for all sintered samples should have an increased influence on dielectric and ferroelectric properties due to strain effects between ferroelectric BaTiO3 and magnetic ferrite phases. This is in accordance with our previous research on the formation of BaTiO3–Fe2O3 core/shell structures, in which we showed that strain originating from the BaTiO3 core strongly affects the electrical properties of the Fe3O4 shell, and vice versa [68].
Mass magnetization values at room temperature for the sintered samples are listed in Table 2. Microstructure (grain size) and phase composition, as well as their interplay guide the magnetization process and influence magnetic properties in general [69]. With an increase in sintering temperature up to 1300 °C, different phase composition was obtained (Table 1) and the microstructure was significantly changed (Figure 3 and Figure 4). In the case of BaTiO3/NiFe2O4 and BaTiO3/ZnFe2O4, the increase in sintering temperature led to the reduction in mass magnetization (ΔM/M0 = 28.7% and ΔM/M0 = 97.8% respectively), while the net magnetization was slightly enhanced for the composite containing mixed Ni,Zn-ferrite (ΔM/M0 = 13.2%).
In the latter case and in comparison, to BaTiO3/NiFe2O4 and BaTiO3/ZnFe2O4, mass magnetization enhancement can be explained by the most significant grain size increment as the sintering temperature increased, Figure 4 and Table 2. The change in mass magnetization value in the temperature range from 20 °C to 600 °C under the magnetic field of 50 kA/m for the sintered samples is presented in Figure 5. Magnetization of BaTiO3/NiFe2O4 and BaTiO3/ZnFe2O4 showed a similar trend upon heating, decreasing slightly, irrespective of sintering temperature. In the case of BaTiO3/Ni0.5Zn0.5Fe2O4 sintered at 1150 °C, there was a sharp fall in mass magnetization due to the phase transition caused by partial destruction of the domain structure within the crystallites from 340 °C to 400 °C, followed by a gentle fall in mass magnetization up to 480 °C. Then, the biggest fall due to thermal effects near Curie temperature (TC) about 540 °C occurred. It was shown that the BaTiO3/NiFe2O4 sintered at 1300 °C has a TC over 600 °C, while the TC value of its analogue sintered at 1150 °C is about 600 °C. In the case of BaTiO3/Ni0.5Zn0.5Fe2O4 sintered at 1300 °C, TC is significantly lower (≈420 °C). This can be explained by the fact that Curie temperature decreases with an increase in Zn content due to the weakening of A-B superexchange interaction caused by the replacement of Fe3+ by Zn2+ ions at tetrahedral sites.
The relative dielectric constant and the loss tangent as a function of frequency along with corresponding AC conductivity are shown in Figure 6. In the low and mid frequency range, the dielectric constant value decreased with a relatively small slope for all investigated pellets at both sintering temperatures. The reduction in dielectric constant with increasing frequency can be related to Maxwell–Wagner interfacial polarization along with Koop’s phenomenological theory [70,71]. The highest value of dielectric constant was observed for BaTiO3/Ni0.5Zn0.5Fe2O4 sintered at 1150 °C in the low and mid frequency regions, Figure 6a. In particular cases ε’ and tgδ were greatly increased as a consequence of the highest amount of conductive phases since the influence of the spinel phase on dielectric properties is very strong [72]. Further calcination of this sample led to a lower value of the dielectric constant in the same frequency range. The same was observed in the case of BaTiO3/ZnFe2O4, Figure 6a. The dispersion phenomenon in these cases may also originate from the compositional inhomogeneity of formed core/shell structures. The appearance of dielectric relaxation peak at 900 Hz (Figure 6b), recorded for BaTiO3/Ni0.5Zn0.5Fe2O4 sintered at 1150 °C might originate from enhanced Maxwell–Wagner polarization between the BaTiO3 phase with higher resistivity and the conductive oxide phases with much lower resistivity. This is in accordance with the research of Yu et al. where the high value of the dielectric constant with frequency relaxation of the BaTiO3-(Ni0.3Zn0.7)Fe2.1O4 has been attributed to this type of polarization mechanism [72]. In the case of BaTiO3/ZnFe2O4 calcined at the same temperature dielectric relaxation occurred at 90 Hz, Figure 6b. The obtained results are in agreement with phase composition analysis (Table 1) since the dielectric properties of such composites are mainly determined by the amount of conductive oxide phases. The loss tangents for the samples sintered at 1300 °C are lower in comparison to the loss tangents values of samples sintered at 1150 °C in the low and mid frequency range, Figure 6b. This clearly indicates that the temperature of 1300 °C was high enough to achieve a sufficient sintering yielding dense ceramics. The loss tangents graphs revealed the relaxation in the form of maxima at 0.900 MHz, 1.939 MHz, and 2.8461 MHz for BaTiO3/NiFe2O4, BaTiO3/Ni0.5Zn0.5Fe2O4, and BaTiO3/ZnFe2O4 sintered at 1300 °C, respectively, Figure 6b. The increase in sintering temperature up to 1300 °C led to the slightly higher value of dielectric constant for BaTiO3/NiFe2O4 in the frequency range between 1 kHz and 1 MHz, Figure 6a. In the high-frequency region abrupt change of dielectric constant was observed for all samples sintered at 1300 °C, indicating strong frequency dependence, Figure 6a. Generally, the dielectric behaviour of samples sintered at 1300 °C is nearly the same in comparison to their analogues sintered at 1150 °C as a consequence of decreased inhomogeneity in formed core/shell structures. The obvious frequency dispersion in ε’ detected for all sintered pellets was caused by the inhomogeneous structure of the spinel phases. A more pronounced effect was evident for BaTiO3/Ni0.5Zn0.5Fe2O4 and BaTiO3/ZnFe2O4, corroborating EDS maps where a higher level of localized ferrite shells occurred, Figure 3 and Figure 4.
Figure 6c shows variations in AC conductivity as a function of frequency for the investigated samples. It was noticed that the increase of conductive ferrite phases influenced the non-linear deviation, while the AC conductivity non-linearly increased with the increase in the frequency, most probably due to heterogeneous conduction and electronic polarization contribution of the ferrite phases [73,74].
The EIS analyzer software and equivalent circuit consisting of two parallel R-CPE elements connected in series were applied for the investigation of relaxation processes. The representative curve for BaTiO3/NiFe2O4 sintered at 1150 °C, shown in Figure 7, indicates that experimental data can be fitted with two circles whose centers are not located on the Z’ axis. This type of modeled circle is typical for the samples which have no single relaxation time (τ), but several of them whose distribution can be presented with mean relaxation time (τp = ωp−1). This is characteristic of non-Debye relaxation in which the depression angle (θ) relates to the distribution width of the relaxation time due to the non-uniform grain boundary structure of the samples [75]. In our case, non-Debye relaxation originated not only from the porous structure, but from different phases and core-shell structures’ grain boundaries. Therefore, the fitting procedure included the use of two CPE instead of typical RC circuits.
Variations of relative dielectric constant, tangent loss, and AC conductivity with the frequency for the selected temperature range (150–400 K) for all sintered samples are displayed in Figure 8, Figure 9 and Figure 10, respectively. The relative dielectric constant value is continuously reduced, exhibiting a plateau in the high-frequency region, irrespective of the investigated sample, Figure 8. The increase in permittivity in the low-frequency region with an increase in temperature can be addressed by nano-inhomogeneous conductivity of ferrite phases [76,77]. The frequency-dependent tangent loss values for the samples sintered at 1150 °C show a typical behavior of composites with inhomogeneous conductivity. Interestingly, in the case of samples sintered at 1300 °C, in the high-temperature range, the values of high-frequency tangent loss increased due to the defects in the material, including oxygen vacancies and transformation of BaTiO3 from P4mm to P4/mmm space group, Figure 9. From the AC conductivity spectra, presented in Figure 10, it is obvious that the conductivity exhibited a twist of about 104 Hz, deviating from the classical Jonsher relationship [78].
The non-linear dependence in P-E measurements indicated typical behavior for ferroelectric composites where the structure inhomogeneity can lead to uncharacteristic forms of hysteresis loops. This type of inhomogeneity mainly originates from the presence of a large amount of spinel ferrite phase in the core/shell structures and localized regions of agglomerated ferrites.
The P-E loops for all sintered samples at a fixed frequency of 100 Hz and electrical field of 10 kV/cm are given in the Supplementary material (Figure S1), while a typical hysteresis curve for sample BaTiO3/NiFe2O4 sintered at 1150 °C at the fields of 20 kV/cm is presented in Figure 11. In this sample, the amount of ferroelectric BaTiO3 tetragonal (P4mm) phase was 77(2)%, i.e., the highest among all investigated sintered samples, while the amount of conductive ferrite/barioferrite phases was the lowest, Table 1. The increase of the barium-titanate phase led to the decrease of the coercive field. For the BaTiO3/ZnFe2O4 and BaTiO3/Ni0.5Zn0.5Fe2O4 samples sintered at 1150 °C, where the localization of Zn-rich phases has been observed by EDS mappings, hysteresis loops shape was strongly affected by the large amount of conductive phases in the composites (see Figure S1 and Figure 3, and Table 1). The increase in temperature up to 1300 °C led to the transformation of BaTiO3 from P4mm to P4/mmm space group in all three cases, Table 1. The highest amount of non-centrosymmetric phase was observed for BaTiO3/NiFe2O4 sintered at 1300 °C, significantly deteriorating the ferroelectric hysteresis loop, Figure S1. The ferroelectric hysteresis loop shape was mostly influenced in the case of BaTiO3/Ni0.5Zn0.5Fe2O4 sintered at 1300 °C in comparison to its analogue sintered at 1150 °C, since the conductive phases amount was reduced (see Table 1).
The presence of spinel phases alongside with Maxwell-Wagner interfacial polarization influenced the hysteresis loops shapes. Furthermore, the deviation from the ferroelectric behavior of investigated composites might originate from the formation of core-shell structures where ferrite agglomerates surrounded BaTiO3 particles. Therefore, it is very hard to determine the values of saturation polarization and coercive field from the presented ferroelectric loops [79].
The leakage current density (j) as a function of static electric field (E) on semi-logarithmic plots were presented in Figure 12. The highest value of leakage current was obtained for BaTiO3/Ni0.5Zn0.5Fe2O4 sintered at 1150 °C, due to the highest amount of the conductive nickel, and zinc oxide phases, Figure 12a and Table 1. This is in accordance with the dielectric spectra presented in Figure 6b, where the dielectric loss was significant (at 900 Hz). On the other hand, the lowest value of leakage current density was found in the sample with the highest concentration of barium titanate phase (BaTiO3/NiFe2O4 sintered at 1150 °C). The increase in sintering temperature reduced the amount of the conductive nickel zinc oxide phases in BaTiO3/Ni0.5Zn0.5Fe2O4 (see Table 1), leading to a slight decrease of the current leakage, Figure 12.
To illustrate the conduction mechanism in the investigated ceramics, plots log j versus log E were recorded, Figure 13. It should be emphasized that the range of the applied electric field was not the same for all investigated samples due to different compositions and microstructure inhomogeneity. Furthermore, in this type of experiment, the effective distance between the electrodes during the measurements may vary, which could cause dielectric breakdown and additionally complicate the interpretation of the experimental data. Taking all this into account, although many studies explain the conduction in such materials by four possible mechanisms (grain boundary limited conduction (GBLC), ohmic conduction mechanism, space charge limited conduction (SCLC), or trap-controlled SCLC mechanism) [80,81], the measured room-temperature leakage current density and its dependence on the static electric field in such complex composites cannot be easily interpreted. However, the presence of the ohmic conduction mechanism was undoubted for all investigated samples, Figure 13.

3. Materials and Methods

3.1. Synthesis

All chemicals (barium titanate (BaTiO3, 99%), acetylacetone, ammonium hydroxide solution (28% NH3 in water), iron(III) chloride hexahydrate (FeCl3·6H2O, 98%), nickel(II) chloride hexahydrate (NiCl2·6H2O, 98%), zinc(II) chloride (ZnCl2, 98%), toluene (99.8%)) were obtained from Sigma-Aldrich.
All investigated ferrites (NiFe2O4, ZnFe2O4, Ni0.5Zn0.5Fe2O4) were in situ prepared on BaTiO3 particles by thermal decomposition method from appropriate acetylacetonate complexes ([Fe(acac)3], [Ni(acac)2], and [Zn(acac)2], where acac presents acetylacetonate anion). The iron(III) acetylacetonate, nickel(II) acetylacetonate, and zinc(II) acetylacetonate were synthesized in a reaction of appropriate metal ions (Fe3+, Ni2+, Zn2+) with ammonium acetylacetonate. The synthesis procedure for obtaining such ferrite systems was previously described by Andjelkovic et al. [82]. Briefly, a stoichiometric amount of BaTiO3 and appropriate acetylacetonate complexes necessary to obtain 0.013 mol of ferrite/titanate composite were used. The thermal decomposition of the mixture suspended in toluene was performed in an electrical furnace with a heating rate of 10 °C/min at t = 500 °C for 1 h, followed by pulverization in an agate mortar.
After the initial preparation protocols, the as-prepared powders were compressed into the pellets at 300 MPa using a uniaxial double action pressing process with an 8 mm diameter tool, hydraulic press RING, P-14, and VEB THURINGER. The pellets were sintered at the temperatures of 1150 °C and 1300 °C in an electrical tube furnace equipped with a LAND calibration source, with a heating rate of 15 °C/min to 1000 °C and 5 °C/min until chosen temperatures were reached for 2.5 h. The sintered samples were removed from the electrical tube furnace after spontaneously cooling to room temperature.

3.2. Characterization

X-ray powder diffraction (XRPD) patterns were collected using Ultima IV Rigaku diffractometer with CuKα1,2 radiation (U = 40.0 kV, I = 40.0 mA) equipped with D/TeX Ultra high—speed detector. The diffraction angle range was 10–80° 2θ with a step of 0.02°. at a scan speed of 5°/min. The phase composition of the synthesized materials, as well as, phase abundances are calculated by the RIR method incorporated in PDXL2 integrated X-ray powder diffraction software (Version 2.8.30; Rigaku Corporation, Tokyo, Japan).
The morphology and composition of the prepared composites were determined by scanning electron microscopy (SEM) performed on JEOL JSM-6390 LV coupled with electron dispersive spectroscopy (Oxford Instruments X-MaxN). The accelerating voltage was in the range of 20 and 30 kV.
Mass magnetization measurements were performed according to a modified Faraday method using a laboratory weighing scale (Sartorius PRACTUM 124-1S) with a sensitivity of 10−7 kg and a magnetic field strength at the sample placement site of 50 kA/m. The heating rate was 20 °C/min.
Dielectric properties of the sintered samples were determined by two digital LCR meters: Hameg 8118 (from 20 Hz to 90 kHz) and Agilent 4285A (from 90 kHz to 9 MHz), under normal atmospheric pressure, ambient temperature, and relative humidity of 40%. The applied voltage across the closed micrometer capacitor cell was 1.5 V. The capacitor cell was housed in a Faraday cage. To obtain broader frequency dependence of dielectric parameters (tg δ, ε’, Z’, Z”), frequency spectra were merged.
To perform temperature dependence measurements pellets were placed in a vacuum chamber with a cold head and capacitor cell mounted on it. Pfeiffer vacuum turbo molecular pump maintained 10−4 mbar pressure. CTI Cryogenics refrigerating system model 22 mounted on the cold head was applied to a lower temperature to 150 K. Lakeshore 340 temperature controller with hater attached at the cold head was used to gradual heating rate of 2.5 K/min up to 400 K.
Ferroelectric and leakage current measurements were conducted in the electrical field range of 5–40 kV/cm on the Precision Multiferroic Test System with High Voltage Interface (Radiant Technologies, Inc., Albuquerque, New Mexico).

4. Conclusions

The aim of this study was the investigation of the effect of phase composition on the magnetic, dielectric, and ferroelectric properties of BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1) ceramic composites. Powders, NiFe2O4, ZnFe2O4, and Ni0.5Zn0.5Fe2O4, were in situ synthesized by thermal decomposition of acetylacetonate precursors onto BaTiO3 surface and additionally sintered at two chosen temperatures (1150 °C and 1300 °C) to obtain dense ceramics. Since phase composition and morphology have a significant influence on the material functional properties, the XRPD, as well as SEM was performed and the results were evaluated in detail. Generally, the spinel and perovskite phases were dominant for as-prepared materials, while spinel, perovskite, and barioferrite-like phases in different ratios prevailed in the case of sintered samples. Although the final sintering stage was not reached at both chosen temperatures, a significantly better sintering effect was noticed at 1300 °C, especially in the composite containing mixed Ni,Zn-ferrite where the mass magnetization was slightly enhanced with an increase in sintering temperature. It was concluded that the dielectric and ferroelectric properties of investigated composites are mainly determined by the amount of conductive oxide phases, the formation of core-shell structures, and microstructure inhomogeneity.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/inorganics11020051/s1, Figure S1: Electrical hysteresis loops for sintered samples.

Author Contributions

Conceptualization, L.A.; Methodology, M.Š. and L.A.; Investigation, M.Š., I.P., M.M.M., A.D., A.K., V.B.P., A.K.-G. and L.A.; Resources, M.Š., I.P., M.M.M., A.D., A.K., V.B.P., A.K.-G. and L.A.; Writing—Original Draft, M.Š. and L.A.; Writing—review and editing, M.Š., V.B.P. and L.A.; Supervision, L.A. All authors have read and agreed to the published version of the manuscript.

Funding

The authors would like to thank the Ministry of Education, Science and Technological Development of Republic of Serbia (Grant Nos. 451-03-68/2022-14/200026, 451-03-68/2022-14/200126, 451-03-68/2022-14/200162, 451-03-68/2022-14/200053, 451-03-68/2022-14/200017, 451-03-68/2022-14/200132 and 451-03-68/2022-14/200116) for financial support.

Data Availability Statement

No new data were created or analyzed in this study. Data sharing is not applicable to this article.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. XRPD of BaTiO3/NiFe2O4, BaTiO3/ZnFe2O4, and BaTiO3/Ni0.5Zn0.5Fe2O4 samples.
Figure 1. XRPD of BaTiO3/NiFe2O4, BaTiO3/ZnFe2O4, and BaTiO3/Ni0.5Zn0.5Fe2O4 samples.
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Figure 2. SEM and EDS layered images of non-sintered BaTiO3/NiFe2O4, BaTiO3/ZnFe2O4, and BaTiO3/Ni0.5Zn0.5Fe2O4 samples (Ba-cyan; Zn-yellow; Ni-orange; Fe-magenta; Ti-blue; O-green).
Figure 2. SEM and EDS layered images of non-sintered BaTiO3/NiFe2O4, BaTiO3/ZnFe2O4, and BaTiO3/Ni0.5Zn0.5Fe2O4 samples (Ba-cyan; Zn-yellow; Ni-orange; Fe-magenta; Ti-blue; O-green).
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Figure 3. SEM and EDS layered images of BaTiO3/NiFe2O4, BaTiO3/ZnFe2O4, and BaTiO3/Ni0.5Zn0.5Fe2O4 samples sintered at 1150 °C (Ba-cyan; Zn-yellow; Ni-orange; Fe-magenta; Ti-blue; O-green).
Figure 3. SEM and EDS layered images of BaTiO3/NiFe2O4, BaTiO3/ZnFe2O4, and BaTiO3/Ni0.5Zn0.5Fe2O4 samples sintered at 1150 °C (Ba-cyan; Zn-yellow; Ni-orange; Fe-magenta; Ti-blue; O-green).
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Figure 4. SEM and EDS layered images of BaTiO3/NiFe2O4, BaTiO3/ZnFe2O4, and BaTiO3/Ni0.5Zn0.5Fe2O4 samples sintered at 1300 °C (Ba-cyan; Zn-yellow; Ni-orange; Fe-magenta; Ti-blue; O-green).
Figure 4. SEM and EDS layered images of BaTiO3/NiFe2O4, BaTiO3/ZnFe2O4, and BaTiO3/Ni0.5Zn0.5Fe2O4 samples sintered at 1300 °C (Ba-cyan; Zn-yellow; Ni-orange; Fe-magenta; Ti-blue; O-green).
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Figure 5. Temperature dependence of mass magnetization in the applied magnetic field of 50 kA/m for all sintered samples.
Figure 5. Temperature dependence of mass magnetization in the applied magnetic field of 50 kA/m for all sintered samples.
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Figure 6. (a) Relative dielectric constant and (b) tangent loss as a function of frequency with (c) AC conductivity for sintered materials. (BaTiO3/NiFe2O4—black, BaTiO3/ZnFe2O4—blue, and BaTiO3/Ni0.5Zn0.5Fe2O4—red.
Figure 6. (a) Relative dielectric constant and (b) tangent loss as a function of frequency with (c) AC conductivity for sintered materials. (BaTiO3/NiFe2O4—black, BaTiO3/ZnFe2O4—blue, and BaTiO3/Ni0.5Zn0.5Fe2O4—red.
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Figure 7. Nuqist plot for BaTiO3/NiFe2O4 sintered at 1150 °C.
Figure 7. Nuqist plot for BaTiO3/NiFe2O4 sintered at 1150 °C.
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Figure 8. Relative dielectric constant spectra of the sintered samples and their temperature dependence.
Figure 8. Relative dielectric constant spectra of the sintered samples and their temperature dependence.
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Figure 9. Tangent loss as a function of the frequency of the sintered samples and its temperature dependence.
Figure 9. Tangent loss as a function of the frequency of the sintered samples and its temperature dependence.
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Figure 10. Conductivity spectra of the sintered samples and their temperature dependence.
Figure 10. Conductivity spectra of the sintered samples and their temperature dependence.
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Figure 11. Hysteresis loop of BaTiO3/NiFe2O4 sintered at 1150 °C at 20 kV/cm field.
Figure 11. Hysteresis loop of BaTiO3/NiFe2O4 sintered at 1150 °C at 20 kV/cm field.
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Figure 12. Leakage current measurements for the samples (a) sintered at 1150 °C, (b) sintered at 1300 °C (BaTiO3/NiFe2O4—black, BaTiO3/ZnFe2O4—blue, and BaTiO3/Ni0.5Zn0.5Fe2O4—red) as log j—E dependence.
Figure 12. Leakage current measurements for the samples (a) sintered at 1150 °C, (b) sintered at 1300 °C (BaTiO3/NiFe2O4—black, BaTiO3/ZnFe2O4—blue, and BaTiO3/Ni0.5Zn0.5Fe2O4—red) as log j—E dependence.
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Figure 13. Leakage current measurements for the samples (a) sintered at 1150 °C, (b) sintered at 1300 °C (BaTiO3/NiFe2O4—black, BaTiO3/ZnFe2O4—blue, and BaTiO3/Ni0.5Zn0.5Fe2O4—red) as log j—log E dependence; n represents the slope of the curves in logarithmic plots.
Figure 13. Leakage current measurements for the samples (a) sintered at 1150 °C, (b) sintered at 1300 °C (BaTiO3/NiFe2O4—black, BaTiO3/ZnFe2O4—blue, and BaTiO3/Ni0.5Zn0.5Fe2O4—red) as log j—log E dependence; n represents the slope of the curves in logarithmic plots.
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Table 1. The phase composition of prepared composites. In parenthesis next to the phase chemical formulae crystal system and space group are presented as well as corresponding PDF card numbers from the ICDD database. Phase abundances are calculated by the RIR method.
Table 1. The phase composition of prepared composites. In parenthesis next to the phase chemical formulae crystal system and space group are presented as well as corresponding PDF card numbers from the ICDD database. Phase abundances are calculated by the RIR method.
SamplesPhase
BaTiO3/NiFe2O4
as-prepared
BaTiO3
Tetragonal (P4mm)
PDF # 01-078-2738
57(2)%
Ni1.3Fe1.7O4
Spinel (Fd-3m)
PDF # 01-080-0072
43(2)%
/
BaTiO3/ZnFe2O4
as-prepared
BaTiO3
Tetragonal (P4mm)
PDF # 01-081-8524
66.3(6)%
ZnFe2O4
Spinel (Fd-3m)
PDF # 01-083-442
29.4(5)%
ZnO
Wurtzite (P63mc)
PDF # 01-070-8070
4.3(2)%
BaTiO3/Ni0.5Zn0.5Fe2O4
as-prepared
BaTiO3
Tetragonal (P4mm)
PDF # 01-083-8300
60(1)%
NixZn1−xFe2O4
Spinel (Fd-3m)
PDF # 01-080-4511
40(1)%
BaTiNiFe10O19 (P63/mmc)
PDF # 00-054-0776
>1%
BaTiO3/NiFe2O4
1150 °C
BaTiO3
Tetragonal (P4mm)
PDF # 01-083-8300
77(2)%
Ni1.25Fe1.85O4
Spinel (Fd-3m)
PDF # 01-088-0380
19(2)%
BaFe11.9O19/
BaTiNiFe10O19
PDF # 01-079-1742/00-054-0776
(P63/mmc)
4(1)%
BaTiO3/ZnFe2O4
1150 °C
BaTiO3
Tetragonal (P4mm)
PDF # 00-005-0626
50(5)%
ZnFe2O4
Spinel (Fd-3m)
PDF # 01-078-5429
46(4)%
BaTi0.636Fe0.364O2.804
PDF # 01-089-4607
4(1)%
BaTiZnFe10O19
PDF # 00-054-1246
>1%
BaTiO3/Ni0.5Zn0.5Fe2O4
1150 °C
BaTiO3
Tetragonal (P4mm)
PDF # 01-074-4540
40(1)%
NixZn1−xFe2O4
Spinel (Fd-3m)
PDF # 01-077-9652
24(1)%
BaTiNiFe10O19 (P63/mmc)
PDF # 00-054-0776
>1%
Ni0.8Zn0.2O
PDF # 01-071-6735
36(1)%
BaTiO3/NiFe2O4
1300 °C
BaTiO3
Tetragonal (P4/mmm)
PDF # 01-079-2264
71.1(4)%
Ni0.4Fe2.6O4
Spinel (Fd-3m)
PDF # 01-087-2335
23.5(3)%
BaFe0.67Ti0.33O2.952
PDF # 01-089-0949
(P63/mmc)
5.4(5)%
BaTiO3/ZnFe2O4
1300 °C
BaTiO3
Tetragonal (P4/mmm)
PDF # 01-079-2264
63.5(3)%
ZnFe2O4
Spinel (Fd-3m)
PDF # 01-078-5429
29.6(2)%
BaFe0.125Ti0.875O2.92
(P63/mmc)
PDF # 01-089-4605
6.9(3)%.
BaTiO3/Ni0.5Zn0.5Fe2O4
1300 °C
BaTiO3
Tetragonal (P4/mmm)
PDF # 01-079-2264
56(3)%
Ni0.8Zn0.2Fe2O4
Spinel (Fd-3m)
PDF # 01-077-9719
34(3)%
BaFe0.25Ti0.75O2.888
(P63/mmc)
PDF # 01-089-4604
9(1)%
Ni0.02Zn0.98O
PDF # 01-080-3507
1.0(1)%
Table 2. Mass magnetization values of sintered samples at room temperature.
Table 2. Mass magnetization values of sintered samples at room temperature.
SampleM [emu/g]
BaTiO3/NiFe2O4 1150 °C12.46
BaTiO3/ZnFe2O4 1150 °C1.74
BaTiO3/Ni0.5Zn0.5Fe2O4 1150 °C17.26
BaTiO3/NiFe2O4 1300 °C9.26
BaTiO3/ZnFe2O4 1300 °C0.06
BaTiO3/Ni0.5Zn0.5Fe2O4 1300 °C17.91
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MDPI and ACS Style

Šuljagić, M.; Petronijević, I.; Mirković, M.M.; Kremenović, A.; Džunuzović, A.; Pavlović, V.B.; Kalezić-Glišović, A.; Andjelković, L. BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1) Composites Synthesized by Thermal Decomposition: Magnetic, Dielectric and Ferroelectric Properties. Inorganics 2023, 11, 51. https://doi.org/10.3390/inorganics11020051

AMA Style

Šuljagić M, Petronijević I, Mirković MM, Kremenović A, Džunuzović A, Pavlović VB, Kalezić-Glišović A, Andjelković L. BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1) Composites Synthesized by Thermal Decomposition: Magnetic, Dielectric and Ferroelectric Properties. Inorganics. 2023; 11(2):51. https://doi.org/10.3390/inorganics11020051

Chicago/Turabian Style

Šuljagić, Marija, Ivan Petronijević, Miljana M. Mirković, Aleksandar Kremenović, Adis Džunuzović, Vladimir B. Pavlović, Aleksandra Kalezić-Glišović, and Ljubica Andjelković. 2023. "BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1) Composites Synthesized by Thermal Decomposition: Magnetic, Dielectric and Ferroelectric Properties" Inorganics 11, no. 2: 51. https://doi.org/10.3390/inorganics11020051

APA Style

Šuljagić, M., Petronijević, I., Mirković, M. M., Kremenović, A., Džunuzović, A., Pavlović, V. B., Kalezić-Glišović, A., & Andjelković, L. (2023). BaTiO3/NixZn1−xFe2O4 (x = 0, 0.5, 1) Composites Synthesized by Thermal Decomposition: Magnetic, Dielectric and Ferroelectric Properties. Inorganics, 11(2), 51. https://doi.org/10.3390/inorganics11020051

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