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Article

Synthesis of (Bi2O3)1-x(PbO)x Thin Films by Plasma-Assisted Reactive Evaporation

by
Aleksandras Iljinas
1,
Vytautas Stankus
1,*,
Darius Virbukas
1 and
Remigijus Kaliasas
2
1
Department of Physics, Kaunas University of Technology, Studentu Str. 50, LT-51368 Kaunas, Lithuania
2
Technology Science Faculty, University of Applied Sciences, Laisvės Sq. 23, LT-35200 Panevėžys, Lithuania
*
Author to whom correspondence should be addressed.
Coatings 2025, 15(7), 748; https://doi.org/10.3390/coatings15070748
Submission received: 18 April 2025 / Revised: 11 June 2025 / Accepted: 20 June 2025 / Published: 24 June 2025
(This article belongs to the Special Issue Advances in Novel Coatings)
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Abstract

Thin, dense and nanocrystal bismuth oxide films were prepared by the in situ plasma-assisted reactive evaporation (ARE) method using lead doping. Thin films were deposited at room temperature and at 500 °C temperature on glass and silicon substrates. X-ray diffraction, SEM, EDS, and optical measurements were applied to characterize these bismuth oxide films. The results showed that it is possible to synthesize the δ-Bi2O3 phase thin films at a temperature lower than 729 °C using an plasma-assisted reactive evaporation (ARE) method and stabilize it (to room temperature) using the additives of lead oxide. The influence of lead oxide concentration on phase formation was investigated. The optimal amount of lead oxide dopant was determined. An excess of lead oxide concentration forms PbO and δ-Bi2O3 mixture phases and nanorods appear in films. The synthesized δ-Bi2O3 phase was metastable; it transformed into the β-Bi2O3 phase after thermal impact during impedance measurements. The cross section of thin film sample shows the dense and monolithic structure. Optical measurements show that the optical band gap increases with increasing lead concentration. It was found that the highest total ionic conductivity of (Bi1−xPb0.26)2O3 is 0.165 S/cm at 1073 K temperature and activation energy is ΔEtot = 0.5 eV.

1. Introduction

Oxide materials exhibiting ion conductivity have been widely studied due to their relevance in solid oxide fuel cells, sensors, and other electrochemical devices. These materials have been synthesized using various methods such as physical and chemical vapor deposition atomic layer deposition (ALD) [1,2], PVD [3,4] and CVD [5,6], sol–gel [7,8] and pulsed laser deposition [9,10]. Bismuth oxide (δ-phase) exhibits the highest known oxide ion conductivity (~0.1–1.0 S/cm, 700–800 °C) [11,12,13,14,15] among known ceramic materials, sometimes even an order of magnitude higher than YSZ ((ZrO2)1−x(Y2O3)x) (~0.01 S/cm, 700–800 °C) [16], doped ceria (Ce0.8 Gd0.2O2−δ, CeO5Sm2, Ce0.9Y0.1O2) (~0.01–0.1 S/cm, 700–800 °C) [17] or lanthanum gallate-based perovskites (La(1−x)Sr(x)Ga(1−y)Mg(y)O(3−δ)) (~10−1 S/cm at 700–800 °C) [18].
However, its practical application is restricted by its thermal instability, requiring stabilization through doping. The significant polymorphism of bismuth oxide, with at least nine known polymorphic phases, along with its thermal instability and property changes over long-term storage, makes studying its characteristics highly challenging [19,20,21]. The defective fluorite structure of δ-Bi2O3 has a very high vacancy concentration and it seeks half vacancies per metal atom. This feature, in combination with the high polarizability of bismuth, leads to the very high oxide ion conductivity of this phase [22]. These properties make bismuth oxide one of the most perspective candidates for application in optoelectronics, solar cells, sensors and solid oxide fuel cells (SOFCs). The main problem is that the δ-Bi2O3 phase is stable between 729 °C and 817 °C [22]. During the process of cooling, the δ-Bi2O3 phase transforms to a mixture of low-temperature phases (α, β, γ) and the ionic conductivity drops to the few orders [13,22]. δ-Bi2O3 can be stabilized at room temperature by adding various oxides [23,24,25,26]. The valency of substituting cations is the main factor for δ-phase stabilization. Many researchers try to use rare earth metals as having an ionic radius comparable to Bi3+ [11,24,25,27]. The results of these investigations are not very encouraging. The main requirements for electrolytes, until now, have not been reached (films need to be dense, have ion conductivity that is as high as possible and show good stability in both reducing and oxidizing environments). As a result, more possibilities are not well investigated.
Stabilizing the delta (δ) phase of Bi2O3, especially at room temperature, is a key area of research. Lead (Pb) is not typically used as a dopant for this purpose. Instead, elements like rare earths (e.g., Y, Gd, Sm, Er, Ho, Tb, Nd, Pr) [28] and other metals (e.g., Nb, Zr, Ta) [29,30,31] are commonly employed to stabilize the δ-phase in Bi2O3. While co-doping with different elements can enhance stability and conductivity, lead’s role in this context is less established compared to other dopants. The type of structure formed depends on the dopant type (primarily the ionic radius of the dopant) and the concentration. Replacing some Bi3+ atoms in the crystal lattice with Pb2+ atoms, which have lower valence and a closer ion radius, introduces defects (oxygen vacancies) or strains that stabilize (prevent the transition from the high-temperature phase to the low-temperature phase) the desired crystal (FCC) structure (δ-phase) in thin films. Oxygen vacancies reduce lattice distortion and allow for a stable cubic or tetragonal phase at room temperature [13,32,33].
When heated in air, vacuum, or different gases, bismuth oxide polymorphs exhibit a diverse range of phase transformation pathways. These transformations depend on the initial phase composition of the material and various experimental parameters specific to each production method [19,20,21,34,35,36,37,38,39,40,41,42]. Thermal evaporation is a commonly used method for thin films involving the deposition of low-melting-point materials [43]. The bismuth and lead have low melting points at 271.5 °C and 327.5 °C, respectively, but the reaction rate between bismuth or lead and oxygen is very low. So, the presence of the reactive oxygen gas in the vacuum chamber for bismuth oxide film growth is not enough for its oxidation. The extra speed of oxidation processes is needed. For this reason, a plasma-assisted reactive evaporation method in this work was used. The vapor ionization and the plasma potential can increase the kinetic energy of the vapors from 0.2 eV to 5.0 eV and increase the reaction rate between the vapor atoms and reactive gases. Plasma was formed by exited electrons, ionized vapor and reactive gas atoms [44,45]. The reactive plasma-assisted thermal evaporation technique allows for the production of a high volume of uniform, dense and high-adhesive films. The deposition process is easily controlled, and high deposition rates are achieved. This technique allows us to directly deposit the Bi2O3 films and eliminates the need for an additional oxidation procedure. There are no provided studies using this method for the formation of delta Bi2O3 films by the additives of PbO.
The aim and novelty of this work is to synthesize the δ-Bi2O3 phase thin films at temperatures lower than 729 °C using an in situ plasma-assisted reactive evaporation method and stabilize it (to room temperature) using the additives of lead oxide. The optimal amount of lead oxide dopant for the stabilization of the cubic phase was determined. The phase, structure, morphology, optic properties and ion conductivity of (Bi2O3)1−x(PbO)x thin films were investigated.

2. Materials and Methods

The (Bi2O3)1−x(PbO)x thin films with various mole fractions were deposited onto soda lime glass (Superior Marienfeld company microscope slides, Lauda-Königshofen, Germany) and Si (100) substrates by reactive plasma-assisted thermal evaporation in an O2 gas environment (pressure of 4 Pa) from molybdenum evaporation boat. Metallic Bi and Pb pieces (Kurt J. Lesker Company, Jefferson Hills, PA, USA (both of 99.999% purity) were mixed and thermally melted in the molybdenum evaporation boat and used as the evaporated material. The formation of the films was performed at 25 °C (room temperature) and 500 °C. Before deposition, the glass substrates were cleaned ultrasonically using acetone for 20 min and dried in a nitrogen flow. The Si substrates were cleaned in diluted HF acid for 1 min and in de-ionized water for 1 min, and dried in a nitrogen flow. The deposition conditions of the films are summarized in Table 1. The O2 plasma was generated between the resistively heated molybdenum boat shield and substrate holder. The distance between the boat shield and substrate was 10 cm. The substrate holder was heated and negatively biased during deposition; the bias voltage was 400 V.
The surface morphology of the samples was analyzed using scanning electron microscopy (SEM) (RAITH-e-LiNE, Raith GmbH, Dortmund, Germany). The SEM images were performed at the voltage of 10 kV and distance of 5.6 mm and 10.6 mm, respectively. The elemental compositions of the deposited (Bi2O3)1−x(PbO)x structures were measured by energy dispersive spectrometry (EDS) (Bruker AXS from GmbH, Bruker corporation, Billerica, MA, USA). Measurements were performed from 1.05 mm2 surface area using 10 kV at 5 different points and the average values were calculated. The crystallographic structure of thin films was investigated by XRD (Bruker D8 series diffractometer, (Bruker, Bruker, Billerica, MA, USA) using monochromatic CuKα (0.154059 nm) radiation with Bragg–Brentano geometry. The peaks were analyzed using WinFit software (WinFit, V 1.2) and the average size of thin film crystallites was determined from the peak broadening by the single-line and multiple-line analyses and was checked using the Scherrer equation:
D = K λ β c o s θ
where D is the mean crystallite size, λ is diffraction wavelength, β is the line broadening at full width at half maximum after subtracting the instrumental line broadening, θ is the diffraction angle and K is a dimensionless shape factor, with a value close to unity. A shape factor of 0.9 was used. The transmittance and reflectance spectra of the films were measured at normal incidence with a UV–VIS–NIR spectrophotometer (Ocean Optics USB4000, Ocean Optics, Inc., Dunedin, FL, USA). The absorption edge of the transmittance spectra was analyzed using the Tauc method; optical band gap Eg was also determined then.
The electrical properties were investigated by ProboStat (NORECS AS, Sandvika, Norway), which used a function of (0.1 Hz to 1 MHz) frequency at different temperatures (1073–473) K with 20-degree increments. The platinum electrodes (diameter 5.5 mm) were formed on the electrolyte before the measurement, and the impedance spectrum was measured in-plane. The impedance spectrum was analyzed using Z-view2 software and the conductivity was estimated using relation (2),
σ = L S R
where L is the thin films thinness, S is the electrode area and R the resistance obtained from the impedance spectra.

3. Results and Discussions

The bismuth oxide (without Pb) orange-yellow transparent thin film was synthesized on a glass substrate at room temperature. The XRD profile shows that the film has an amorphous structure (Figure 1). It is common when the oxide’s thin films grow by reactive depositions on unheated substrates to become amorphous because the energy for the formation of the crystal structure is too low. The doping of PbO induces the thin film crystallization process. The XRD pattern shows that the lead-doped bismuth oxide phase can be identified as the body-centered cubic (bcc) (Pn3m) structure with the peaks at 2θ = 27.94°, 32.40°, 46.73°, 55.12° and 58.05° corresponding to (111), (200), (220), (311) and (222) orientation of the single γ-Bi2O3 phase (JCPDS data file No. 00-027–0052). No separate lead or lead oxide phases were detected, although EDS analysis shows Pb/Bi atomic ratio of 0.22 (it corresponds to (Bi2O3)0.82(PbO)0.18 or 18% of PbO molar concentration). The XRD pattern analysis demonstrated the mixture of amorphous and nanocrystallite phases (the main peak is broadened and is on the hump, representing amorphous phase). The average size of crystallites was 14 nm.
The formation, crystallization, morphology, phase transition, optic and electrical properties at higher temperatures and different PbO concentrations were investigated. The temperature of the substrate during deposition was changed to 500 °C. Using soda lime glass as a substrate, because of structural deformation, sodium ion diffusion and stress from expansion risk, 500 °C is the highest optimal temperature. It should be mentioned that without Pb dopants, performing the deposition at 500 °C produces the typical β-Bi2O3 phase. EDS analysis for these films shows Pb/Bi atomic ratios of 0.36, 0.19 and 0.16 (it corresponds to 0.15, 0.08 and 0.06 PbO mole fractions or (Bi2O3)0.85(PbO)0.15, (Bi2O3)0.92(PbO)0.08 and (Bi2O3)0.94(PbO)0.06). XRD patterns of thin films deposited at 500 °C on glass substrates show that a single nanocrystalline phase of δ-Bi2O3 was formed (Figure 2). The amorphous matrix disappeared. This phase can be identified as the face-centered cubic (fcc) (Fm3m) structure with the peaks at 2θ = 27.87°, 32.40°, 46.40°, 54.94° and 57.61° corresponding to (111), (200), (220), (311) and (222) orientation of single δ-Bi2O3 phase (JCPDS data file No. 47-1056). The crystallite size does not depend on the PbO concentration and was determined as 29 nm. There is no physical reason for the dependence of the crystallite size on the substitution of an element with a dopant (Pb) in the crystal lattice at a low concentration. It is seen that a tetragonal PbO peak appears at a 15% PbO concentration, and a mixture of δ-Bi2O3 and PbO phases was obtained (Figure 2). N.M. Sammes [13] showed in the phase diagram that mixtures of Bi2O3 and PbO result in the δ-Bi2O3 phase when the PbO molar concentration is in a range from 5% to 30%, and when PbO exceeds 30%, the mixture of two phases appears. In our case, the increase in PbO amount in films shows the decrease in the δ-Bi2O3 phase (Figure 2). The temperature of crystallization of δ-Bi2O3 phase was 200 °C lower than reported (700 °C) in diagram [13]. It can be explained that additional energy, needed for δ phase formation, is taken from plasma. Positive oxygen ions bombard the growing thin film with an energy of 400 eV [44].
XRD patterns of thin films, deposited at 500 °C on Si substrates, show similar results as on glass, but with a more expressed peak of (200) orientation (Figure 3). EDS analysis for these films shows Pb/Bi atomic ratios of 0.42, 0.31, 0.26 (it corresponds to 0.17, 0.15 and 0.13 PbO mole fractions or (Bi2O3)0.83(PbO)0.17, (Bi2O3)0.85(PbO)0.15 and (Bi2O3)0.87(PbO)0.13). Despite the fact that all evaporation parameters were the same (including the weighted amount of Bi and Pb) for both types of substrates, the mole fractions of films deposited on Si are different than films deposited on glass. The explanation of it can be performed due to the different desorption rates of Pb on Si and on glass at relatively high substrate temperatures (which is above the melting temperature of Pb—327.5 °C). The same single-nanocrystalline phase of δ-Bi2O3 as on the glass substrate was formed. Increasing the lead oxide concentration from 13% to 17% reduces the size of crystallites from 29 nm to 25 nm. A thin film with 17% lead oxide also has one small peak, which can be identified as tetragonal PbO.
This decrease can be explained only by the appearance and growth of secondary PbO phase crystallites, which limits the growth of the δ-Bi2O3 phase in whole-material volume. Therefore, we can state that the δ-Bi2O3 phase, using this method, can be formed in a narrow window of concentration (from 6 to 13%). Until 6%, the δ-Bi2O3 phase does not form, and over 13%, the secondary PbO phase begins to appear. As was mentioned above, compared to N.M. Sammes [13], the δ-Bi2O3 phase exists when PbO molar concentration is in the range of 5% to 30% and when PbO exceeds 30% the mixture of two phases appears. Our window is narrower.
SEM images of prepared samples on glass substrates at various PbO concentrations are shown in Figure 4.
It is shown that at PbO mole fraction x = 0.06 film consists of ~140 nm size grains (Figure 4a,d). It disagrees with the XRD results of crystallites’ size, and therefore it can be stated that the grains consist of nanocrystallites (~29 nm). It can be seen that the film structure is pure-grained without any amorphous matrix. The formed grain sizes are smaller when the PbO mole fraction increases to x = 0.08 (Figure 4b,e), but are aggregated in bigger conglomerates. Smaller grain sizes form because the Pb or PbO melting point temperature is larger than Bi or Bi2O3; therefore, the nucleation centers formation ratio is larger than the grain growth ratio. Films with an excess of the PbO component (15%) consisting of grain structure mixed with nanorods rudiments are shown in Figure 4c,f. One-dimensional nanorod growth starts when the growth becomes anisotropic. During the growth of bismuth oxide nanorods, the perpendicular substrate direction had the minimum surface free energy, and this implied that the c-axis of the films was the thermodynamically favorable orientation. This process is influenced by crystallographic anisotropy of growth oxide, surface diffusion, oxygen pressure and substrate effects (surface energy and lattice matching). It corresponds to the results of the PbO nanorod formation possibility of other authors [37,46,47].
Independently, the XRD patterns of thin films on glass and silicon substrates show similar results, and the morphology on silicon substrates is different. The SEM image of x = 0.13 (Figure 5a,d) shows a grained film structure that is similar to x = 0.08 on glass, but with a smaller size of grains (~ 100 nm), containing ~ 29 nm crystallites. The image of x = 0.15 (Figure 5b,e) shows a dense and expressed cubic nanocrystalline structure. They are similar, like x = 0.15 on glass, but denser and more developed nanorods are shown (Figure 5c,f (x = 0.17)). The form and dimension of nanorods are the same on the Si substrate and glass. However, the density of nanorods amount on the glass substrate is higher. This was undoubtedly due to the different substrate types, which have different adsorption and surface diffusion coefficients at the relatively high substrate temperatures (which is above melting temperature (327.5 °C) of Pb) of Pb adatoms on glass and Si; therefore, we observe different sizes and densities of nanorods.
The cross section of the sample (x = 0.13) was made because no PbO excess was in the sample. The dense and monolithic structure is seen in Figure 6.
In summary, we can describe (Figure 7) the dynamics of the formation of the crystal phase in (Bi2O3)1−x(PbO)x thin films, which obey the Stranski–Krastanov growing mode [48], where two competing processes are involved—2D layer and 3D island growth. The grain sizes, obtained from the SEM results, depend on surface diffusion and growing center concentrations, which at the same temperature, depend on adatom type, concentration and substrate type. Firstly, the adsorbed lead adatoms, of which the surface diffusion coefficient is different from bismuth and the concentration is changing, influence the growing columnar grain size. Secondly, changing the substrate from glass to silicon also changes the surface diffusion coefficient.
Optical measurements were carried out on deposited on glass samples. The calculated results of the curve (αhν)2 = f(hν) show that the optical band gap increases from 2.55 eV to 2.68 eV (Figure 8) with an increasing lead oxide concentration (from 6% to 15%). This indicates that the optical absorption edges shift to a higher photon energy. This is possible due to the lead oxide band gap (2.8 eV) [49], which is larger than bismuth oxide (2.3–2.6 eV) [40]; therefore, the rise of the lead oxide concentration could form the larger band gap of thin film. This confirms the presence of lead oxide in samples.
Ionic conductivity at different temperatures was estimated from the impedance spectra of (Bi2O3)0.87(PbO)0.13 thin film. The impedances recorded in a complex plane Z” = f(Z’) at 500 K, 520 K and 540 K temperatures are shown in Figure 9. The relaxation frequency (fR) at different temperatures was obtained from the impedance spectra too. The grain circular arc is very small compared with the grain boundary arc; therefore, only one circular arc is seen. This means that it is possible to only determine the total ionic conductivity. The total resistance was calculated using the following equation Rtot = Rg + Rgb from the resistance of grains (Rg) and grain boundaries (Rgb). The capacity and resistivity were estimated using Z-view2 software fitting results. It was estimated that resistivity decreases and capacity increases with the increasing temperature, and the relaxation frequency shifts to a higher frequency region at higher temperatures (values are shown in Figure 9).
The total ionic conductivity depends on the mobility of oxygen ions through vacancies, total concentration of ions, valence of the oxygen vacancies and electrical charge. We can claim that the conductivity depends on the mobility of ions, whereas temperature changes (in the range of 500–540 K) do not influence the valence, the charge or the concentration of charge carriers.
(Bi2O3)0.87(PbO)0.13 thin films total conductivity vs. 1000/T data is shown in Figure 10. The total ionic conductivity is composed of grain and grain boundary conductivities. Ionic conductivity and activation energy depend on the phase of bismuth oxide. The highest ionic conductivity and activation energy of the δ-Bi2O3 phase are 0.09 S/cm and 0.5 eV, respectively [13]. It was found that the highest total ionic conductivity of (Bi2O3)0.87(PbO)0.13 is 0.165 S/cm at 1073 K temperature and activation energy ΔEtot = 0.5 eV. Different activation energies were achieved at different temperature ranges. The total conductivity rapidly decreased at temperatures lower than 1120 K and it is the transition from delta to beta phase. The δ-phase transitions to the β2-phase approximately at 730–560 °C (1–1.2 of 1000/T). The β2-phase starts to decompose into the β-phase (Bi2O3)0.87(PbO)0.13 at approximately 560–400 °C. XRD measurements of the same sample after annealing show that the thin film is transformed into the α-Bi2O3 phase. It shows that the synthesized δ-Bi2O3 phase was thermodynamically metastable. We think that plasma energy, a high growing rate, a high deposition temperature (500 °C) and PbO dopants, which distort the crystal lattice, create thermodynamically favorable conditions for the formation of metastable δ-Bi2O3 phase.

4. Conclusions

The results showed that it is possible to synthesize the δ-Bi2O3 nanostructure phase thin films at lower than 729 °C temperature using in situ plasma-assisted reactive evaporation method and stabilize it (to room temperature) using the additives of lead oxide. The optimal amount of lead oxide dopant was determined. XRD measurements have shown that the samples deposited on glass and silicon substrates exhibit a similar δ-Bi2O3 oxide phase. The results showed that crystallite sizes, surface morphology and optical properties depend on lead oxide concentration in films. The crystallite sizes do not depend on the lead concentration when using glass substrates and decrease (from 29 to 25 nm) on Si substrates when concentration increases (from 13% to 0.17%). The best phase crystal structure forms at least 13% lead concentration on Si substrate. SEM measurements showed that the concentration of lead influences the sizes of grains by up to a limit (to 15% on glass and to 17% on Si) when PbO and δ-Bi2O3 mixture phases and nanorods in films appear. In summary, the results showed that there is a narrow window of lead dopant concentration (6%–13%), less for which β-Bi2O3 exists and more of which δ-Bi2O3 phase breaks down to PbO and decreasing crystallites of δ-Bi2O3. The cross section of the thin-film sample shows the dense and monolithic structure. Optical measurements show that the optical band gap increases (from 2.55 eV to 2.68 eV) with the increase in the lead concentration. The highest ionic conductivity of (Bi2O3)0.87(PbO)0.13 is 0.165 S/cm at 1073 K temperature and activation energy ΔEtot = 0.5 eV and it is dependent on the phase. The synthesized δ-Bi2O3 phase was metastable; it transformed into the β-Bi2O3 phase after thermal impact during impedance measurements.

Author Contributions

Conceptualization, A.I. and V.S.; methodology, A.I. and V.S.; validation, A.I. and V.S.; investigation, A.I., V.S., D.V. and R.K.; writing—original draft preparation, A.I. and V.S.; writing—review and editing, A.I., vs. and D.V. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in the study are included in the article, and further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. XRD diffraction patterns of pure bismuth oxide and lead oxide doped (Bi2O3)0.82(PbO)0.18 bismuth oxide thin films deposited on glass substrate at room temperature.
Figure 1. XRD diffraction patterns of pure bismuth oxide and lead oxide doped (Bi2O3)0.82(PbO)0.18 bismuth oxide thin films deposited on glass substrate at room temperature.
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Figure 2. X-Ray diffraction patterns of (Bi2O3)1−x(PbO)x thin films deposited on glass substrate at 500 °C.
Figure 2. X-Ray diffraction patterns of (Bi2O3)1−x(PbO)x thin films deposited on glass substrate at 500 °C.
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Coatings 15 00748 g003
Figure 3. X-Ray diffraction patterns of (Bi2O3)1−x(PbO)x thin films deposited on Si substrate at 500 °C.
Figure 3. X-Ray diffraction patterns of (Bi2O3)1−x(PbO)x thin films deposited on Si substrate at 500 °C.
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Figure 4. The SEM images of (Bi2O3)1−x(PbO)x thin films deposited on glass substrates at 500 °C (a–c) with grain size distribution shown in (d–f).
Figure 4. The SEM images of (Bi2O3)1−x(PbO)x thin films deposited on glass substrates at 500 °C (a–c) with grain size distribution shown in (d–f).
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Coatings 15 00748 g005
Figure 5. The SEM images of (Bi2O3)1−x(PbO)x thin films deposited on silicon substrates at 500 °C (a–c) with grain size distribution shown in (d–f).
Figure 5. The SEM images of (Bi2O3)1−x(PbO)x thin films deposited on silicon substrates at 500 °C (a–c) with grain size distribution shown in (d–f).
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Figure 6. SEM cross section image of (Bi2O3)0.87(PbO)0.13 thin film deposited on Si substrate at 500 °C.
Figure 6. SEM cross section image of (Bi2O3)0.87(PbO)0.13 thin film deposited on Si substrate at 500 °C.
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Figure 7. Mechanism of formation of crystal phase in (Bi2O3)1−x(PbO)x thin films according to Stranski–Krastanov. (a) initial monolayer growth; (b) changes into island growth after a few monolayers; (c) a competition between two growth mechanisms.
Figure 7. Mechanism of formation of crystal phase in (Bi2O3)1−x(PbO)x thin films according to Stranski–Krastanov. (a) initial monolayer growth; (b) changes into island growth after a few monolayers; (c) a competition between two growth mechanisms.
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Figure 8. Plot of (αhν)2 against hν of (Bi2O3)1−x(PbO)x thin films on glass substrate at 500 °C.
Figure 8. Plot of (αhν)2 against hν of (Bi2O3)1−x(PbO)x thin films on glass substrate at 500 °C.
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Figure 9. The impedance plots at 500 K, 520 K and 540 K temperatures of (Bi2O3)0.87(PbO)0.13 thin films.
Figure 9. The impedance plots at 500 K, 520 K and 540 K temperatures of (Bi2O3)0.87(PbO)0.13 thin films.
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Figure 10. Arrhenius plots for total conductivity of (Bi2O3)0.87(PbO)0.13 thin films.
Figure 10. Arrhenius plots for total conductivity of (Bi2O3)0.87(PbO)0.13 thin films.
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Table 1. The deposition parameters and their values.
Table 1. The deposition parameters and their values.
Parameters
SubstrateSi (100)Glass
Mass of Bi pieces, mg400390360400390360400
Mass of Pb pieces, mg100130150100130150140
Mass ratio of evaporated mix of pieces (Pb/Bi)0.250.330.420.250.330.420.35
Thickness of thin film, nm293337382311359397423
Atomic ratio of Pb/Bi in deposited films0.260.310.420.160.190.360.22
Mole fraction in deposited films of (Bi2O3)1−x(PbO)x0.130.150.170.060.080.150.18
Substrate temperature, °C50025
Evaporation rate, mg/min50
Initial pressure, Pa5 × 10−3
Pressure of reactive O2 gas, Pa4
Distance between the boat and the substrate, cm10
Plasma discharge and bias voltage, V400
Discharge current, A0.625
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Iljinas, A.; Stankus, V.; Virbukas, D.; Kaliasas, R. Synthesis of (Bi2O3)1-x(PbO)x Thin Films by Plasma-Assisted Reactive Evaporation. Coatings 2025, 15, 748. https://doi.org/10.3390/coatings15070748

AMA Style

Iljinas A, Stankus V, Virbukas D, Kaliasas R. Synthesis of (Bi2O3)1-x(PbO)x Thin Films by Plasma-Assisted Reactive Evaporation. Coatings. 2025; 15(7):748. https://doi.org/10.3390/coatings15070748

Chicago/Turabian Style

Iljinas, Aleksandras, Vytautas Stankus, Darius Virbukas, and Remigijus Kaliasas. 2025. "Synthesis of (Bi2O3)1-x(PbO)x Thin Films by Plasma-Assisted Reactive Evaporation" Coatings 15, no. 7: 748. https://doi.org/10.3390/coatings15070748

APA Style

Iljinas, A., Stankus, V., Virbukas, D., & Kaliasas, R. (2025). Synthesis of (Bi2O3)1-x(PbO)x Thin Films by Plasma-Assisted Reactive Evaporation. Coatings, 15(7), 748. https://doi.org/10.3390/coatings15070748

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