Bi2O3-Modified Ceramics Based on BaTiO3 Powder Synthesized in Water Vapor

Bi2O3 was investigated in the role of a modifier for BaTiO3 powder synthesized in a water vapor atmosphere at 200 °C and 1.55 MPa. Modification was aimed at increasing the sinterability of the powder as well as improving the structural and dielectric properties of the obtained ceramics. The morphology and phase contents of the synthesized BaTiO3 powder were controlled by the methods of SEM and XRD. Properties of pure and Bi-doped BaTiO3 ceramics were comprehensively studied by XRD, SEM, dielectric spectroscopy, and standard approaches for density and mechanical strength determination. Doping with Bi2O3 favored BaTiO3 ceramic densification and strengthening. The room-temperature dielectric constant and the loss tangent of Bi-doped BaTiO3 were shown to stabilize within the frequency range of 20 Hz to 2 MHz compared to non-doped material. The drop of dielectric constant between room temperature and Curie point was significantly reduced after Bi2O3 addition to BaTiO3. Bi2O3 appeared to be an effective modifier for BaTiO3 ceramics produced from non-stoichiometric powder synthesized in water vapor.


Introduction
Barium titanate BaTiO3 is an important ferroelectric widely applied in the production of ceramic components for numerous microelectronic devices such as multilayer ceramic capacitors (MLCC), piezoelectric transducers, positive temperature coefficient resistors (PTCR), actuators, etc. [1][2][3][4]. The ferroelectric properties of BaTiO3 originate from spontaneous polarization and appear in its crystals on cooling to a certain temperature (Curie temperature, TCurie = 120-130 °C) corresponding to cubic to tetragonal phase transition. This kind of polarization in BaTiO3 is caused by displacement of Ti 4+ ions from the central positions of cubic unit cells during their transformation to tetragonal cells. These displacements occur unidirectionally within certain crystalline regions called ferroelectric domains. Neighboring domains compensate each other's polarizations owing to their different directions. When an electric field is applied, a spontaneous polarization vector follows the electric field vector in ferroelectric crystals [5]. The most attractive properties of BaTiO3 are the low Curie temperature and high dielectric constant accompanied by relatively low loss tangent. BaTiO3 ferroelectric phase transition corresponds to a rise of dielectric constant up to several thousands. This order of magnitude is maintained by the dielectric constant down to ambient temperature.
One of the main challenges of BaTiO3 ceramics production is achieving high material density close to its theoretical value [6]. The density is determined by the microstructure of the ceramics. Structural inhomogeneity related to porosity as well as trace amounts of moisture which is inevitably closed into the pores cause the increase of ceramic conductivity and worsen its functional properties. Controlled dispersity of the starting BaTiO3 powder and tuned technological parameters of ceramic manufacturing would allow obtaining dense material with low structure defectiveness as desired for MLCCs and other devices [7].
A known approach to modification of oxide ceramic properties is the use of different oxide additives [8][9][10]. Their incorporation into the initial lattice may affect the rates of sintering and grain growth or lead to liquid phase formation. Additives which form high-temperature melts provide wetting of the individual starting particles and formation of concave necks between them. Capillary forces pull the particles together, yielding in powder compaction. The melt facilitates mutual orientation of the particles, increases the contact area between them, and promotes shrinkage of the sample. Chemical interaction of the additive and the main component intensifies solid-state mobility in a compact and reduces the activation energy of volume and surface diffusion during the sintering. As a result, obtaining a material with increased density and strength is expected.
A method of BaTiO3 synthesis in water vapor atmosphere was proposed in recent works [11][12][13][14][15]. In contrast to the traditional hydrothermal method which is usually based on a reaction between the species in a solution, this method of synthesis includes the treatment of an initially dry barium and titanium oxides mixture in water vapor in equilibrium with liquid. Having an advantage over the hydrothermal route, the synthesis in water vapor leads to lower water and hydroxyl group contents in the product and results in narrower BaTiO3 crystal size distribution [13]. The method is ecologically benign owing to the mild conditions of the synthesis and high atomic efficiency. The obtained BaTiO3 powder performed high sinterability under spark plasma sintering (SPS) conditions [14]. The corresponding ceramics possessed a homogenous microstructure, submicron grain size, and a dielectric constant of 1500-2300 at room temperature at 1 MHz. However, when sintered by the more available and widespread conventional route, ceramics based on BaTiO3 synthesized in vapor conditions achieved lower density and had insufficient dielectric properties [12].
In the present work steps were taken to improve the microstructural and dielectric properties of these BaTiO3 ceramics by modification of the initial powder composition. One of the typical modifications of BaTiO3 ceramics is incorporation of Bi 3+ ions [16][17][18][19][20][21][22]. As reported earlier, the use of Bi2O3 additive to BaTiO3 powder promoted ceramic densification owing to liquid phase formation during the sintering [23][24][25]. Bi 3+ ion is known to substitute aliovalently Ba 2+ in a perovskite lattice because of similar ionic radii (0.145 and 0.160 nm, respectively) [18,[23][24][25][26][27]. The solubility limit of Bi 3+ in BaTiO3 was reported to reach 5 at % [28]. The charge compensation mechanism leads to formation of barium vacancies which promote solid-state mobility and consequently decrease the energy required for sintering [18]. BaTiO3 modification with Bi 3+ ions is used industrially to lower its sintering temperature [18,19]. Besides, Bi-doping plays an important role in modification of the dielectric properties of BaTiO3-based ceramics, for instance, in flattening of its dielectric response in a certain temperature range, and in turning its behavior to relaxor ferroelectric or n-type semiconducting [27,[29][30][31]. Bi2O3 is often used in the production of complex oxide dielectric compositions such as solid solutions or layered structures with tuned dielectric characteristics [16].
Bi2O3 addition was expected to facilitate the sintering of BaTiO3 powder synthesized in water vapor atmosphere, favor the formation of a homogenous microstructure, and raise its dielectric properties to the desired level.

BaTiO3 Powder Characterization
BaTiO3 synthesis was carried out from a mixture of barium and titanium oxides which was treated in a water vapor atmosphere at a temperature of 200 °C and a corresponding autogenous pressure of 1.55 MPa for 20 h. The phase composition of the synthesized powder turned out to be sensitive to the molar ratio of initial oxides in the reaction mixture ( Figure 1, Table 1). A significant amount of unreacted TiO2 was found in a product synthesized from an equimolar mixture of BaO and TiO2 (sample BT-100). Traces of rutile were also detected in powders produced with the use of excessive BaO amounts relatively to TiO2 (Ba/Ti = 1.10 and 1.20, samples BT-110 and BT-120). Unreacted barium compounds were removed from the product by washing with acetic acid solution and distilled water. Single-phase BaTiO3 was obtained from a mixture of simple oxides with Ba/Ti = 1.25 (sample BT-125). The detected peaks corresponded to cubic BaTiO3 modification. Metastability of this phase (also called pseudocubic) below the temperature of phase transition to tetragonal modification (TCurie = 120-130 °C) could be explained by the influence of the remaining structural hydroxyl groups and charged defects which deteriorated the spontaneous polarization [32]. A detailed examination of the background found no minor phases in the sample BT-125 (Figure 1, inset). Incomplete transformation of the reagents observed when lower BaO excess was used can be attributed to the diffusion factor governing BaTiO3 formation in water vapor conditions. Single-phase BaTiO3 powder is preferable for subsequent ceramic processing [7]. The sample BT-125 was subsequently used in ceramic manufacturing.  1.25 100.0 0.0 XRF analysis of the single-phase BaTiO3 powder (sample BT-125) revealed barium ion deficiency towards stoichiometry (determined ratio Ba/Ti = 0.82). This effect was explained by the particular leaching of Ba 2+ ions from the surface of the powder while being washed in acid solution after the synthesis [14]. Barium leaching has often been observed in BaTiO3 particles synthesized in solution by hydrothermal or related techniques because of high defectiveness and chemical activity of their surface [33][34][35]. Figure 2 shows the morphology and particle size distribution of the sample BT-125. The powder consisted of agglomerated round-shaped particles with a total mean size of 110 nm.

Phase Composition of Bi2O3-Modified BaTiO3 Ceramics
XRD patterns of pure and Bi-doped barium titanate ceramics are shown in Figure 3. The main component of the prepared ceramic samples was tetragonal BaTiO3 (Figure 3). Along with this phase, X-ray patterns contained minor peaks of barium polytitanates, i.e., BaTi2O5 and BaTi4O9. Secondary phases found in the non-modified BaTiO3 ceramics as well as in the samples with comparatively low addition of Bi2O3 (up to 0.5 mol %) could be explained by the non-stoichiometry of the starting powder. The lack of A-site ions in perovskite ABO3 structure of the synthesized powder caused formation of Ti-rich phases during the sintering. However, the increase in Bi2O3 initial amount to 2.5-5.0 mol % was accompanied by smoothing of minor phase peaks which pointed to lowering of their contents ( Figure 3a). This can be attributed to partial occupation of vacant A-positions in perovskite by Bi 3+ ions. Barium substitution by bismuth easily occurred in the studied conditions owing to the BaTiO3 initial non-stoichiometry.
The changes in phase composition of ceramics at a fixed level of doping (0.5 mol % Bi2O3) and varied sintering temperature are presented in Figure 3b. Raising of the sintering temperature led to disappearance of some secondary phase peaks. However, traces of BaTi2O5 were detected in the sample sintered at 1250 °C ( Figure 3b).
The changes of BaTiO3 unit cell parameters with the increase in Bi-doping resulted in a complicated character which originated from the initial non-stoichiometry of the perovskite-type oxide ( Figure 4). In non-doped BaTiO3, the presence of negatively charged Ba 2+ -vacancies was presumed to be compensated by the positive charge of oxygen vacancies. This type of defectiveness can lead to the shrinkage of the unit cell in comparison to "ideal" BaTiO3 crystal. Incorporation of Bi 3+ ions into vacant Ba 2+ positions and simultaneous elimination of oxygen vacancies, which occurred according to the equation (follows Kroger-Vink notation): Bi2O3 → 2 BiBa • + VBa'' + 3 OO × , resulted in a notable increase in both a and c parameters of the BaTiO3 tetragonal cell. This was notably manifested in the case of 0.1 mol% Bi2O3 addition and was also accompanied by a leap of tetragonality c/a. Besides barium vacancy occupation, Bi 3+ ions promoted further elongation of the c parameter of BaTiO3 cell because of the polarization effect of its lone electron pair on the off-centered Ti 4+ ion [20]. Doping with higher amounts of Bi2O3 maintained a certain concentration of barium vacancies while oxygen vacancy concentration was expected to decrement gradually. The observed dependence of BaTiO3 lattice parameters and tetragonality on Bi2O3 content exceeding 0.5 mol % was in line with the data reported earlier for stoichiometric Bi-doped BaTiO3 ceramics [20].  EDX mapping of a fracture surface of BaTiO3 ceramics doped with 5.0 mol % Bi2O3 revealed homogenous distribution of all contained elements including bismuth ( Figure 5). Bismuth ions appeared to substitute barium in its positions uniformly over the whole grains of BaTiO3. This kind of Bi 3+ distribution was reported for BaTiO3-based ceramics with a comparable doping level [36,37].  Figure 6a shows the effect of the Bi2O3 additive amount on BaTiO3 ceramic density. In the series of ceramic samples sintered at 1200 and 1225 °C, the relative density passed through a maximum with increasing Bi2O3 content. After the sintering at 1200 °C, the highest density of 4.88 g cm −3 was achieved at 2.5 mol % Bi2O3. Sintered at 1225 °C, the ceramics performed the highest densification up to 5.17 g cm −3 when doped with 0.1 mol % Bi2O3. When modified with 5.0 mol % Bi2O3, these ceramics possessed a density comparable to non-doped material. At a higher sintering temperature (1250 °C), the rise of the additive content was accompanied by a monotonic decrease in the density of the ceramics which pointed to an overheating phenomenon. Interestingly, this temperature appeared too low for the sintering of non-doped ceramics. Currently, the relative density of pure BaTiO3 ceramics prepared at 1250 °C has reached only 76.3%. However, previously sintered at 1300 °C, it resulted in a density of 86.0% of theoretical [12]. The highest density among the studied samples reached 86.2% of its theoretical value and was obtained by ceramics sintered at 1225 °C with addition of 0.1 mol % Bi2O3. Passing through a maximum density with increasing bismuth content appeared to be typical for doped BaTiO3 ceramics [23,25]. The currently observed result was comparable to densification of Bi-doped BaTiO3 synthesized by a solid-state method with barium deficiency and sintered in a similar regimen [25].

Structural and Mechanical Properties of Bi2O3-Modified BaTiO3 Ceramics
A pronounced increase in the compressive strength of BaTiO3 ceramics corresponded to low amounts of Bi2O3 additive (Figure 6b). The highest tensile strength after the sintering at 1200 °C was observed when the content of Bi2O3 was 0.5 mol %. Sintering at 1225 and 1250 °C resulted in ceramics with the highest strength in the case of 0.1 mol % Bi2O3. Addition of 0.1 mol % Bi2O3 improved the compressive strength of the ceramics after sintering at 1225 °C to 437 MPa compared to 140 MPa for pure BaTiO3 ceramics manufactured with the same conditions. An increase in Bi2O3 content resulted in no further improvement in the strength characteristics of the material compared to pure BaTiO3 ceramics. Electronic Industries Alliance (EIA) standards for capacitors widely applied by the manufacturers avoid regulation of the mechanical characteristics of the ceramic dielectric layer contained in the device. However, the mechanical strength as well as the dielectric strength are important indicators of capacitor ceramics reliability. Both these properties are very sensitive to the materials' microstructure and change jointly [38,39]. Hence, the value of the mechanical strength can be used as an indirect measure of the dielectric strength of a material. Figure 7 shows the microstructure of BaTiO3 ceramic samples modified with 0.1-0.5 mol % Bi2O3 and resulted in the highest relative density along with a microstructure of pure BaTiO3 ceramics prepared with the same conditions (sintered at 1225 °C for 1 h.). Images of fracture and the surface of pure BaTiO3 ceramics revealed considerable porosity in agreement with the density measurements (Figure 7a,d). The reduction of pore space was revealed as an effect of Bi2O3 addition and was accompanied by an increase in the density of the samples compared to non-doped material. The pores visible in the fractured ceramics containing 0.1 mol % Bi2O3 (Figure 7b) were more numerous than in the sample sintered with 0.5 mol % Bi2O3 (Figure 7c), and more evenly distributed. The surface image of the latter (Figure 7f) revealed small submicron pores neighbored by larger micron-sized ones and voids forming owing to pore coalescence. The sample with 0.1 mol % Bi2O3 was shown to have higher density (Figure 6a). Different character of pore size distribution in the considered samples could affect their mechanical properties in addition to porosity value. Among the parameters determining the strength of a ceramic material, an important role belongs not only to the total value of the porosity but also to the pore-stress interactions determined by the number and the size of pores as well as by the thickness of struts between them [40]. The higher compressive strength achieved by the BaTiO3 sample modified with 0.1 mol % Bi2O3 compared to other samples sintered at 1225 °C could be attributed both to its higher density and uniformity of pore structure.

Dielectric Properties of Bi2O3-Modified BaTiO3 Ceramics
The dielectric properties of pure and Bi2O3-modified BaTiO3 ceramics sintered at 1225 °C are shown in Figure 8. Non-doped ceramics achieved relatively poor dielectric characteristics revealing high sensitivity of the dielectric constant and the loss tangent to the frequency. A-site deficiency and phase inhomogeneity of this sample caused increased concentration of charged defects which resulted in high dielectric losses at low frequencies [41]. Compared to the pure BaTiO3, ceramics prepared with the addition of Bi2O3 achieved more stable values of the dielectric constant and loss tangent within the frequency range of 20 Hz to 2 MHz. The highest room-temperature dielectric constant among the Bi-containing ceramics reached 1310 and was obtained by the sample with addition of 0.1 mol % Bi2O3. Also, this sample was characterized by low loss tangent (0.025-0.038) which slightly varied in the studied frequency range compared to pure BaTiO3. Ceramics doped with 0.1-0.5 mol % Bi2O3 achieved a higher dielectric constant than the non-doped sample in the range of 1-2 MHz.    Table 2). The transition was accompanied by an increase in dielectric constant up to 3253 at 1 kHz. Bi 3+ incorporation into the BaTiO3 structure led to a slight shift of the phase transition point towards higher temperature and to lowering of εmax value. This effect in aliovalently doped perovskite ferroelectrics was usually considered as a diffuse phase transition [23,25,27,[41][42][43]. Bi 3+ ions are known to induce a local electrical field in the volume of BaTiO3 which interacts with the ferroelectric unit cell field and causes dispersion of the phase transition temperature over the sample [23,25,27]. The data reported on Bi 3+ influence on ferroelectric phase transition in BaTiO3-based ceramics appeared to be quite contradictory. Some of the authors noted no diffuse character of the transition for the materials with bismuth content within its solubility limit [26]. However, in other works the diffused behavior even on changing to relaxor type was observed [23,25,27]. Shift of the Curie point and lowering of the corresponding dielectric constant discovered in the current work proved the diffuse nature of the tetragonal to cubic phase transition in BaTiO3 ceramics with addition of Bi2O3. It is practically beneficial leading to a diminished drop of dielectric constant within the working temperature range with the broadening of this range towards higher values.

Discussion
This work provided novel results on the structural and dielectric properties of Bi-doped BaTiO3 ceramics sintered from Ba-deficient powder synthesized in mild conditions of water vapor medium. Previously, non-stoichiometry of the powder was assumed to promote the growth of plate-like abnormal grains in ceramics [44] which led to a non-uniform microstructure and deteriorated the dielectric properties [12]. Currently, Ba 2+ deficit in the synthesized BaTiO3 powder caused secondary polytitanate phase formation during the sintering and increased conductivity which manifested itself in a pronounced frequency dependence of the room-temperature dielectric constant and loss tangent of the ceramics. Addition of Bi 3+ ions to non-stoichiometric BaTiO3 powder allowed slight lowering of the sintering temperature, improvement of the microstructure, achievement of higher phase homogeneity, and stabilization of the dielectric properties of the produced ceramics.
Bismuth oxide is well known as a sintering additive, which helps to increase the density and lower the sintering temperature of various oxide materials. However, in the present work, the introduction of Bi 3+ ions did not always contribute to high densification of the material. The maximum density of the ceramics at a certain Bi 3+ content and its further decrease with increasing doping level were found to be a common pattern at each of the applied sintering temperatures. The position of the maximum density shifted toward higher Bi 3+ concentrations with decreasing sintering temperature. Apparently, an increase in Bi 3+ content within the range of its solubility resulted in a continuous decrease in the optimum sintering temperature of the BaTiO3 ceramics. The samples doped with 0.1 and 0.5% bismuth at 1225 °C as well as the non-doped sample prepared at 1250 °C were believed to be sintered at temperatures close to optimal for their compositions.
Another purpose of Bi2O3 addition to the studied BaTiO3 ceramics was to increase its phase and structural homogeneity. The mechanism of the excess positive charge compensation accompanying Bi 3+ incorporation in A-positions of the perovskite lattice involved binding the available barium vacancies. Because of partial occupation of vacant Ba 2+ positions by Bi 3+ and respective charge balancing, the amount of polytitanate secondary phases in the doped BaTiO3 ceramics was significantly lowered compared to the pure ceramics.
Decreased concentration of charged defects upon the incorporation of Bi 3+ ions in the barium positions in BaTiO3 ceramics caused a reduced sensitivity of the dielectric constant to frequency and lowered the values of the loss tangent. Besides, the excess positive charge of bismuth ions in the A-positions contributed to higher polarization of the Ti 4+ ion and to enhanced ferroelectric properties of the material [25]. The values of the dielectric constant calculated at different temperatures indicated the diffused nature of the ferroelectric phase transition in Bi-doped BaTiO3 ceramics.
Room-temperature values of ε and tgδ obtained in this work for Bi-modified BaTiO3 ceramics corresponded well to the data reported earlier [23,25]. The optimum values were observed in the case of BaTiO3 ceramics sintered at 1225 °C with addition of 0.1 or 0.5 mol % Bi2O3.
Despite a significant improvement in the phase, structural, and dielectric properties of BaTiO3 ceramics resulting from Bi-doping, no appreciable compaction of the material was achieved. A possible solution to this problem would be to increase the sintering duration up to several hours while maintaining the other processing parameters as specified in the current work. However, Bi2O3 proved itself to be an effective additive and modifier for BaTiO3 synthesized in water vapor.

Materials and Methods
Barium titanate powder was synthesized from TiO2 in rutile modification (STP TU KOMP 2-340-11, ≥99.5% purity, Komponent-Reaktiv, Moscow, Russia) and BaO (TU 6-09-03-375-74, ≥98% purity). Starting reagents were mechanically mixed maintaining the molar ratio of Ba/Ti = 1.00; 1.10; 1.20; or 1.25 and subsequently sieved through a nylon sieve (300 µm cell size) three times. The mixture was placed in into a PTFE container inside a stainless-steel autoclave with inner volume of 80 mL. Distilled water in the amount of 21 mL was poured into the autoclave outside the PTFE container. Then, the autoclave was sealed and heated up to 200 °C over 1 h. The corresponding autogenous vapor pressure inside the reactor reached 1.55 MPa. The reaction mixture was held under these conditions for 16 h. After that, the autoclave was rapidly cooled down to room temperature so that the vapor inside it condensed mainly at the bottom, separately from the product. The resulting powder was removed from the opened reactor and washed with a large amount of dilute acetic acid and then distilled water until neutral pH of the solution. The powder was filtered and dried in air at 60-70 °C for 12 h.
Portions of the synthesized BaTiO3 powder were mixed with the calculated amounts of Bi2O3 (VTU 1-48, 99% purity; mean particle size of 10.5 µm, UZHP, Verkhnyaya Pyshma, Russia) in isopropanol medium with the use of planetary ball mill over 30 min at a rate of 300 min −1 . Addition of Bi2O3 amounted to 0.1, 0.5, 2.5, and 5.0 mol % of Bi-ions of their total quantity with Ba-ions in the BaTiO3 sample. After the milling procedure, the obtained mixtures were dried in air at 70 °C for 12 h. and sieved subsequently through sieves with 500 and 1000 µm cell size. To prepare the press-powders, 5 wt % of paraffin was added as a temporary technological binder to each of the samples. The procedure of the binder addition included the steps of paraffin melting, its dilution with ethyl acetate, and addition of the powder to the solution. The obtained slurry was continuously mixed while heating until all the ethyl acetate evaporated. The dry powders covered with paraffin were sieved through a sieve of 500 µm cell size. The prepared press-powders were compacted uniaxially at 100 MPa at room temperature and sintered at 1200, 1225, or 1250 °C in air over 1 h. The sequence of ceramic processing operations is presented schematically in Figure 10. JEOL JSM 6390 LA scanning electron microscope (JEOL Ltd., Tokyo, Japan) was used for investigation of synthesized BaTiO3 powder morphology and microstructure of the manufactured ceramics, as well as for energy dispersive X-ray analysis (EDX) of the ceramics.
X-ray diffraction (XRD) patterns of powder and ceramic samples were registered at Rigaku D/Max-2500 diffractometer (Rigaku Corporation, Tokyo, Japan) with Cu Kα radiation in a range of 10° ≤ 2θ ≤ 70° with a step of 0.02°. Phase contents of the samples were determined by comparison of the experimental patterns with the data of PDF-2 database. GSAS program package [45] was applied for fitting of the diffraction pattern profiles by the Le Bail method and for Rietveld refinement of the unit cell.
X-ray fluorescent (XRF) analysis of BaTiO3 samples was performed at ARL 9900 Workstation spectrometer (Thermo Fisher Scientific Inc., Waltham, MA, USA). The measured data were processed by the fundamental parameters method.
The apparent density of ceramics was estimated by the Archimedes method. The procedure included the following steps. First, dry ceramic samples were weighed (m1-weight of a dry sample). Then, they were weighed dipped in kerosene (m2-weight in liquid) and retrieved therefrom (m3-weight of a sample saturated with liquid). The apparent density was calculated using Equation (1): where ρk is the density of kerosene at the corresponding temperature.
The compression strength of ceramic samples was measured by means of an electromechanical testing machine LFM-C (Walter + Bai AG, Löhningen, Switzerland).
The dielectric properties of the manufactured ceramics were studied with the use of a precision LCR meter Agilent E 4980A (Agilent Technologies, Inc., Santa Clara, CA, USA). The bases of the disc-shaped ceramic samples were polished and painted with silver paste. Then the samples were heated up to 800 °C for 20 min. for metallization. Capacitance measurements were conducted in a frequency range of 20 Hz to 2 MHz at a temperature range of 25 to 150 °C.

Conclusions
The present work achieved an effect of Bi2O3 addition on the properties of ceramics produced from Ba-deficient BaTiO3 powder synthesized in water vapor conditions. Addition of Bi 3+ ions in amounts within the limit of its solubility in BaTiO3 resulted in an improvement of the phase, structural, and dielectric properties of the ceramic material. Occupation of vacant Ba 2+ positions by Bi 3+ ions suppressed formation of polytitanate secondary phases during the sintering. Higher phase homogeneity achieved owing to Bi-doping manifested itself in the uniformity of the ceramic microstructure compared to previous results on sintering of non-doped BaTiO3 ceramics based on this type of initial powder. Incorporation of Bi 3+ ions into the BaTiO3 ceramic structure led to relative stabilization of its dielectric properties (dielectric constant and loss tangent) in a range of 20 Hz to 2 MHz at room temperature. Doping with Bi 3+ caused a slight shift of the BaTiO3 ferroelectric phase transition towards higher temperature as well as lowering of the dielectric constant maximum. The revealed effects defined Bi2O3 as a perspective additive for production of functional ferroelectric ceramics from BaTiO3 powder synthesized in water vapor.