Effect of Al2O3 content on BaO–Al2O3–B2O3–SiO2 glass sealant for solid oxide fuel cell

The glass structure, wetting behavior and crystallization of BaO–Al₂O₃–B₂O₃–SiO₂ system glass containing 2–10 mol% Al₂O₃ were investigated. The introduction of Al₂O₃ caused the conversion of [BO₃] units and [BO₄] units to each other and it played as glass network former when the content was up to 10 mol%, accompanied by [BO₄] → [BO₃]. The stability of the glass improved first and then decreased as Al₂O₃ increased from 2 to 10 mol%, the glass with 5 mol% Al₂O₃ being the most stable one. The wetting behavior of the glasses indicates that excess Al₂O₃ leads to high sealing temperature. The glass containing 5 mol% Al₂O₃ characterized by a lower sealing temperature is suitable for SOFC sealing. Al₂O₃ improves the crystallization temperature of the glass. The crystal phases in the reheated glasses are mainly composed of Ba₂Si₃O₈, BaSiO₃, BaB₂O₄ and BaAl₂Si₂O₈. Al₂O₃ helps the crystallization of BaSiO₃ and BaAl₂Si₂O₈.     

EPR NMR,and XPS study of LaAlO3 phase transition with enhanced magnetic and Faraday rotation properties in glass-ceramics

The phase transition of LaAlO₃ in heavy metal oxide lead-tellurite glass was obtained and verified, along with its influence on glass structure, magnetic, and Faraday rotation properties were characterized through various techniques such as nuclear magnetic resonance (NMR), X-ray neutron diffraction, transmission electron microscopy, X-ray photoelectron microscopy, vibrating-sample magnetometer, and electron paramagnetic resonance (EPR). Cubic LaAlO₃ nanocrystals were synthesized by one-pot hydrothermal technique and doped at 1, 5, 10, and 15 mol% into glasses, respectively. The LaAlO₃ nanocrystals in as-casted glasses were characterized to be around 17 nm in cubic phase belonging to the Pm3m space group. After crystallization treatment at 360 °C for 2 h, cubic LaAlO₃ phases were changed to 14–27 nm-rhombohedral phases due to the temperature-induced viscosity and strain in the melt. The phase transition yielded great modification to the glass structure through converting TeO₄→TeO₃, AlO₆→AlO_4, BO₄→BO₃, and producing non-bridging oxygen. The LaAlO₃ doping enhanced the diamagnetism of as-casted glasses, but after phase transition, the weak diamagnetic nature was changed to strong ferromagnetism and the magnetization significantly increased with the LaAlO₃ doping amount (M_s =55 emu/g). The mechanism behind magnetic property enhancement was discussed through ²⁷Al NMR and EPR of glasses. The Verdet constant of glass with 10% LaAlO₃ was greatly improved to 175 rad/ T.m at 633 nm which is much higher than the documented values in the literature.     

Effects of Nb2O5 and Gd2O3 doping on boron volatility and activity between glass seals and lanthanum-containing cathode

In planar Solid Oxide Fuel Cells (SOFCs), the boron species volatilize from glass seals, and react with lanthanum-containing cathodes (i.e., La_0.6Sr_0.4Co_0.2Fe_0.8O_3 − δ, LSCF) to form LaBO₃ under cathodic polarization, which decomposes the perovskite structure and consequently decreases the electrochemical activity of cathode. In this study, Nb₂O₅ and Gd₂O₃ are added to an aluminoborosilicate glass to reduce the boron volatility from glass and the reaction between sealing glass and LSCF cathode. Both Nb₂O₅ and Gd₂O₃ doping increases the network connectivity, but Nb₂O₅ doping enhances the [BO₃] → [BO₄] transition and reduces the boron volatility from glass seals, thus effectively suppressing the deposition and poisoning of boron contaminants on the LSCF cathode. However, an obvious degradation of the electrocatalytic activity of LSCF occurs in the presence of Gd₂O₃-doped glass. The relationship between glass structure and glass/cathode interaction has been established to provide useful information for designing stable sealing materials for SOFC applications.     

Band gap tuning of Ga2O3–Al2O3 ceramics

Translucent ceramics comprising monoclinic Ga₂O₃ and non-cubic Ga₂O₃–Al₂O₃ solid solution with a composition of Ga_1.5Al_0.5O₃, GaAlO₃ and Ga_0.4Al_1.6O₃ were fabricated through two-step spark plasma sintering by using calcinated commercial mixture oxide ceramic powders. All sintered ceramics were nearly fully densified, with a relative density exceeding 99.2%. The average grain sizes decreased with increasing Al content. Band gap was tuned from 4.08 to 6.37 eV. The highest total transmittance (73.6% at 1100 nm) was measured in Ga_0.4Al_1.6O₃ ceramics with both hexagonal (rhombohedral) and monoclinic crystal structures and a minimum average grain size of 0.288 ± 0.067 μm. Defect related photoluminescence, measured under excitation by a 254 nm UV lamp in the GaAlO₃ and Ga_0.4Al_1.6O₃ ceramics, lasted more than 15 s after removal of the UV source. These translucent ceramics from Ga₂O₃–Al₂O₃ solid solution provide an alternative form of a potential transparent conducting material.     

Influence of Al2O3/SiO2 ratio in multicomponent LNAS glasses and glass-ceramics on the crystallization behavior,microstructure and mechanical performance

Transparent glass-ceramics containing eucryptite and nepheline crystalline phases were prepared from alkali (Li, Na) aluminosilicate glasses with various mole substitutions of Al₂O₃ for SiO₂. The relationships between glass network structure and crystallization behavior of Li₂O–Na₂O–Al₂O₃–SiO₂ (LNAS) glasses were investigated. It was found that the crystallization of the eucryptite and nepheline in LNAS glasses significantly depended on the concentration of Al₂O₃. LNAS glasses with the addition of Al₂O₃ from 16 to 18 mol% exhibited increasing Q⁴ (mAl) structural units confirmed by NMR and Raman spectroscopy, which promoted the formation of eucryptite and nepheline crystalline phases. With the Al₂O₃ content increasing to 19–20 mol%, the formation of highly disordered (Li, Na)₃PO₄ phase which can serve as nucleation sites was inhibited and the crystallization mechanism of glass became surface crystallization. Glass-ceramics containing 18 mol% Al₂O₃ showed high transparency ～84% at 550 nm. Moreover, the microhardness, elastic modulus and fracture toughness are 8.56 GPa, 95.7 GPa and 0.78 MPa m^1/2 respectively. The transparent glass-ceramics with good mechanical properties show high potential in the applications of protective cover of displays.     

The impact of Gd2O3 on nuclear safety proficiencies of TeO2–ZnO–Nb2O5 glasses: A GEANT4 Monte Carlo study

This work was carried out to specify the effect of Gd₂O₃ on the gamma and neutron radiation shielding capacities of tellurite rich glasses with 75TeO₂+15ZnO+(10-x)Nb₂O₅+xGd₂O₃ (TZNG), where (x = 0, 1, 1.5, 2 and 2.5 mol%) nominal composition. The mass attenuation coefficients (μ/ρ) of the studied glasses were acquired with GEANT4 Monte Carlo codes and the results were found to match the theoretical Phy-X values. Next, the variables of Effective atomic number (Z_eff), Half Value Layer (HVL) and Mean Free Path (MFP) were calculated employing μ/ρ values. According to the corollaries, the increment of Gd2O3 insertion to the tellurite based glasses was enhanced the μρ and Z_eff values for total photon, electron, proton and alpha interactions whereas it was dropped the HVL and MFP values. It is also observed that the total stopping powers of the glasses for electron interaction were declined. The geometric progression (GP) approximation was employed to determine the exposure buildup factor (EBF) for the proposed glasses. The EBFs showed the lowest values for TZNG-E glass with 2.5% mole Gd₂O₃ addition. Finally, the fast neutron reduction capacity of the TZNG glasses was surveyed by calculating the effective removal cross-sections (Σ_R) of the glasses. It is determined that the Σ_R values increased with enhancing Gd₂O₃ content since the addition of Gd₂O₃ increased the glass density. Consequently, the TZNG-E glass with the highest Gd₂O₃ additive is the more skillful nominee for gamma-ray and neutron security applications among the investigated glasses.     

Thermal and structural modification in transparent and magnetic germanoborate glasses induced by Gd2O3

A series of new transparent and magnetic germanoborate glasses in the system (100-x)[60GeO₂–25B₂O₃–10Na₂O–4Al₂O₃–1PbO] – (x) Gd₂O₃, with x = 0, 1, 2, 5, 10, 15 and 20 mol%, was prepared and studied with respect to their thermal and structural changes in the presence of Gd₂O₃. Based on Differential Scanning Calorimetre (DSC) analysis, a glass with 5% of Gd₂O₃ showed a high thermal stability, which progressively decreases for samples with higher content of Gd₂O₃. By the analysis of Raman and Fourier Transform Infrared (FTIR) spectra, it was possible to identify that by increasing the amount of Gd₂O₃, a progressive depolymerization of 6-membered Ge^[IV] rings is promoted, concomitant with an increase of Ge^[IV] tetrahedra units with non-briding oxygens. The structural analysis through the local-sensitive techniques EXAFS (Extended X-ray Absorption Fine Structure) and XANES (X-ray Absorption Near Edge Structure) showed that the short-range structural modification around the elements Ge and Gd³⁺ does not change with the addition of Gd₂O₃ and the presence of germanium four-fold coordination [Ge^IV] and Gd³⁺ states, respectively. A simulation of the coordination number (N), the interatomic distance (R) of Ge–O and Gd–O bonds and the Debye-Waller factor was also carried out. The microstructure_, after crystallization, of the sample with 15 mol% of Gd₂O₃ was evaluated using optical and electron microscopes. Finally, the paramagnetic behaviour and ion probe quantification of Gd³⁺ ions were obtained based on magnetic susceptibility measurements.     

Structural modification associated with Al2O3 addition in oxyfluoride glasses: Thermal and mechanical properties

In this work, the effect of gradual addition of Al₂O₃ substituting SiO₂ on the structural, thermal, and mechanical properties of SiO₂–BaF₂–K₂O–GdF₃–Sb₂O₃‐based oxyfluoride glasses have been studied. The X‐ray diffraction (XRD) patterns and differential scanning calorimetric (DSC) curves indicate that there is a distinct primary crystallization corresponding to BaGdF₅ phase formation in the samples without (0AlG) and with 5 mol% substitution of Al₂O₃ (5AlG) while the sample with 10 mol% of Al₂O₃ (10AlG) does not show such crystallization event. Further, the activation energy (E_a) for fluoride crystal formation is higher for the 5AlG in comparison to the 0AlG glass as determined by Kissinger, Augis‐Bennett and Ozawa models. Fourier transform infrared (FTIR) and Raman spectroscopy analysis confirmed the structural modification with the gradual addition of Al₂O₃ in the glass matrix revealing dominant presence of AlO₄ tetrahedral units in 10AlG sample unlike in 5AlG sample which exhibited the manifestation of AlO₆ units. Such structural variation has further been substantiated from the estimated elastic properties like Young's modulus (E), shear modulus (G), bulk modulus (K), longitudinal modulus (L), and mean ultrasonic velocity (U_m) by showing a decrease for 5AlG sample in comparison with 0AlG sample followed by subsequent increase for 10AlG sample.     

Crystallization kinetics of La2O3–Al2O3–B2O3 glass–ceramic composites

One glass formulation (L2 glass) with the composition of La₂O₃, Al₂O₃ and B₂O₃ in a molar ratio of 10:10:80 was selected to cofire with Al₂O₃ filler. The composites underwent a two-stage crystalline evolution in the temperature range of 800 to 975 °C. The crystallization kinetics of LaBO₃ grains and the transformation to LaAl₂B₃O₉ phase were investigated by DTA, XRD, SEM/EDS, and TEM. The results showed that the Al₂O₃ filler plays an important role as the heterogeneous sites of LaBO₃ nuclei, and as reactant for the formation of flaky LaAl₂B₃O₉ crystals. The apparent activation energy of LaBO₃-phase formation in L2 glass was 534 kJ/mol and reduced to 466 kJ/mol by the addition of Al₂O₃. The detail transformation reactions, kinetics, and the crystalline orientation relationship between those phases are reported.     

Joining of Al2O3 to ZTA using a B2O3–Al2O3–SiO2 glass with in-situ precipitated whiskers

A novel B₂O₃–Al₂O₃–SiO₂ (BAS) glass filler was first developed to join Al₂O₃ and zirconia toughened alumina (ZTA) ceramics. The microstructure, crystallization products, and interfacial reaction layer of the joint were all studied. Detailed growth process and the microstructural evolution mechanism of aluminum borate (Al₁₈B₄O₃₃ and Al₄B₂O₉) crystal whiskers were revealed through controlling the joining temperature and the holding time. The results showed that the Al₁₈B₄O₃₃ and Al₄B₂O₉ whiskers formed at the interfaces and in the joining seam, owing to the reaction between the substrates and the BAS glass system, and the precipitation out of the glass, respectively. Finally, bonded with this BAS glass filler at 1400 °C for one hour, the joints exhibited a maximum shear strength of 42 MPa at room temperature and good mechanical performance after thermal cycling.     

Y3Al5O12–SiO2 Glasses: Structure and Polyamorphism

Aerodynamic levitation and CO₂ laser melting have been used to synthesize the yttrium aluminosilicate glasses zY₂O₃–yAl₂O₃–xSiO₂ with z/y = 3/5 corresponding to the YAG (Y₃Al₅O₁₂) composition and x between ~5 and ~45 mol%. The low‐ and high‐density (LDA inclusion and HDA matrix) polyamorphic phases in glasses with less than ~14 mol% SiO₂ were identified with backscattering electron imaging. Polarized and depolarized Raman spectra show the formation of various Qⁿ SiO₄ species whose relative populations change smoothly as the SiO₂ content is altered. The AlOs (s = 4–6) and YOz (z = 6–9) polyhedra formed in the YAG glass are preserved upon silica additions while the terminal oxygens of the Q²AlO₄ tetrahedra are gradually bridged to the Qⁿ‐SiO₄ species. The low‐frequency Boson Peak overlaps with the vibrational spectrum and its maximum is redshifted with increasing silica content. Micro‐Raman spectra measured for the LDA and HDA amorphous phases are found to be similar to the spectra of the bulk glass indicating common structural characteristics. The stability of the LDA phase against crystallization appears to be lower than that of the HDA phase. The crystallinity on certain inclusions consisted of YAG microcrystals and a new unidentified microcrystalline phase within Y₄Al_2(1?x)Si_2xO_(9+x) solid solution.     

Understanding the structure,thermal, and optical properties in Al2O3-incorporated La2O3-TiO2-Nb2O5 glasses

Glasses in the 30La₂O₃-40TiO₂-30Nb₂O₅ system are known to have excellent optical properties such as refractive indices over 2.25 and wide transmittance within the visible to mid-infrared (MIR) region. However, titanoniobate glasses also tend to crystallize easily, significantly limiting their applications in optical glasses due to processing challenges. Therefore, the 30La₂O₃-40TiO₂-(30−x) Nb₂O₅-xAl₂O₃ (LTNA) glass system was successfully synthesized using a aerodynamic containerless technique, which improves glass thermal stability and expands the glass-forming region. The effects of Al₂O₃ on the structure, thermal, and optical properties of base composition glasses were investigated by XRD, DSC, NMR, Raman spectroscopy, and optical measurements. DSC results indicated that as the content of Al₂O₃ increased, the thermal stability of the glasses and glass-forming ability increased, as the 30La₂O₃-40TiO₂-25Nb₂O₅-5Al₂O₃ (Nb-Al-5) glass obtained the highest ΔT value (103.5°C). Structural analysis indicates that the proportion of [AlO₄] units increases gradually and participates in the glass network structure to increase connectivity, promoting more oxygen to become bridging oxygen and form [AlO₄] tetrahedral linkages to [TiO₅] and [NbO₆] groups. The refractive index values of amorphous glasses remained above 2.1 upon Al₂O₃ substitution, and a transmittance exceeding 65% in the visible and mid-infrared range. The crystallization activation energies of 30La₂O₃-40TiO₂-30Nb₂O₅ (Nb-Al-0) and Nb-Al-5 glasses were calculated to be 611.7 and 561.4 kJ/mol, and the Avrami parameters are 5.28 and 4.96, respectively. These results are useful to design new optical glass with good thermal stability, high refractive index and low wavelength dispersion for optical applications such as lenses, endoscopes, mini size lasers, and optical couplers.     

Effects of CdF2 and WO3 additions on the microstructural and thermal properties of TeO2–CdF2–WO3 glass system

This paper presents microstructural characterization investigations and the crystallization behavior of some glasses in the ternary TeO₂–CdF₂–WO₃ system. Differential thermal analysis (DTA) showed that the glass forming ability of the ternary TeO₂–CdF₂–WO₃ system which is in between the values of 21 and 34, is lower than most of the studied tellurite glasses. It is possible to obtain amorphous glass structure for the compositions of 0.80TeO₂–0.10CdF₂–0.10WO₃ and 0.75TeO₂–0.10CdF₂–0.15WO₃. On the other hand, the 0.85TeO₂–0.10CdF₂–0.05WO₃ and 0.75TeO₂–0.15CdF₂–0.10WO₃ compositions do not form glass with conventional quenching techniques. During crystallization of these glasses, the formation of the alpha, delta and gamma TeO₂, WO₃ and CdTe₂O₅ phases were observed with the addition of a new unidentified phase. Three compositions of 0.85TeO₂–0.10CdF₂–0.05WO₃, 0.80TeO₂–0.10CdF₂–0.10WO₃ and 0.75TeO₂–0.10CdF₂–0.15WO₃ demonstrated two exothermic peaks in the DTA curves. SEM/EDS investigations confirmed the existence of the alpha, delta and gamma TeO₂, WO₃ and CdTe₂O₅ phases for the annealed glasses. The microstructure of the δ-TeO₂ phase was clearly observed in the as-cast 0.75TeO₂–0.10CdF₂–0.15WO₃ composition.     

Role of Al3+ on tuning optical properties of Ce3+‐activated borosilicate scintillating glasses prepared in air

A colorless Ce³⁺‐activated borosilicate scintillating glass enriched with Gd₂O₃ is successfully synthesized in air atmosphere for the first time. The full replacement of 10 mol% BaO by Al₂O₃, and the partial substitution of 3 mol% SiO₂ by Si₃N₄ in the designed glass composition are crucial for this success. The role of Al³⁺ on tuning the optical properties of Ce³⁺‐activated borosilicate scintillating glass synthesized in air are analyzed by optical transmittance, X‐ray absorption near edge spectroscopy (XANES) spectra, photoluminescence (PL) and radioluminescence (RL) spectra. The results suggest that the stable Ce⁴⁺ ions can be effectively reduced to stable Ce³⁺ ions by the full replacement of BaO by Al₂O₃, and both the PL andRL intensity of the designed borosilicate scintillating glass are enhanced by a factor of 6.7 and 5.2, respectively. The integral RL intensity of the synthesized Ce³⁺‐activated borosilicate scintillating glass is ~17.2%BGO, with a light output of about 1180 ph/MeV. The strategy of substituting BaO by Al₂O₃ will trigger more scientific and technological considerations in designing novel fast scintillating glasses.     

Characteristics of ZnO-based varistor ceramics doped with Al2O3

The influence of Al₂O₃ doping in the range 0.00–0.83 mol% on the microstructure and current–voltage characteristics of ZnO-based varistor ceramics sintered at 1200 °C for 2 h was studied. The threshold voltage V_T (V/mm) increased up to a dopant level of about 0.08 mol% Al₂O₃; the nonlinear coefficient α was significantly increased by additions of up to 0.04 mol% Al₂O₃, although larger additions of Al₂O₃ caused it to decrease; and the leakage current increased sharply with increasing amounts of Al₂O₃. Doping with Al₂O₃ up to about 0.12 mol% Al₂O₃ resulted in a significantly decreased ZnO grain size, which is mainly responsible for the significantly increased threshold voltage, V_T. No ZnAl₂O₄ spinel phase was detected in any of the samples, and EDXS and WDXS analyses showed that most of the added Al₂O₃ distributed between the Zn₇Sb₂O₁₂ spinel phase and the ZnO phase, while only trace amounts were detected in the Bi₂O₃-rich phase. The spinel phase incorporates an appropriate amount of Al₂O₃; however, with an increasing amount of added Al₂O₃, more of it remains outside the spinel phase in the Bi₂O₃-rich liquid, where it can incorporate into the growing ZnO grains at the sintering temperature. The amount of Al in the ZnO grains was determined. A mechanism for the grain growth inhibition resulting from the small amounts of Al₂O₃ in the Bi₂O₃-rich liquid phase is also proposed.     

Effect of Bi2O3 content on sintering and crystallization behavior of low-temperature firing Bi2O3–B2O3–SiO2 glasses

The sintering behavior of a Pb-free Bi₂O₃–B₂O₃–SiO₂ glass system was examined as a function of Bi₂O₃ content. The glass transition temperature and the crystallization temperature of the glasses decreased with different decreasing gradients as the Bi₂O₃ content increased. The change in temperature affected the sintering behaviors of the glasses. In the case of the 40 mol% Bi₂O₃ addition, large pore accompanied over-firing phenomenon was observed when the sample was sintered over the optimum sintering temperature. However, over-firing was not observed in the sample with 45 mol% of Bi₂O₃ because of the crystallized phases during sintering. When the Bi₂O₃ content was 50–55 mol%, the crystallization temperature became lower than the glass transition temperature, which resulted in the crystallization of glass and it hindered densification.     

Synthesis and microstructure of Gd2O3-doped HfO2 ceramics

The effect of Gd₂O₃-doping on the crystal structure, surface morphology and chemical composition of the Gd₂O₃–HfO₂ system is reported. Gd₂O₃–HfO₂ ceramics with variable composition were prepared by varying the Gd₂O₃ composition in the range of 0–38 mol% balanced HfO₂. X-ray diffraction (XRD) analysis indicates that the Gd₂O₃ concentration influences the crystal structure of the Gd₂O₃–HfO₂ ceramics. Pure HfO₂ and Gd₂O₃ crystallize in monoclinic and body centered cubic structure, respectively. The Gd₂O₃–HfO₂ ceramics exhibit mixed monoclinic and fluorite structure when the Gd₂O₃ concentration is varied from 4 to 12 mol%. At 20 mol% of Gd₂O₃, existence of only the fluorite phase was found. Increasing the Gd₂O₃ concentration to 38 mol% results in the formation of single-phase pyrochlore Gd₂Hf₂O₇ (a = 5.258 Å).     

Microstructure and properties of SiCf/SiC composite joints with CaO–Y2O3–Al2O3–SiO2 interlayer

Using CaO, Y₂O₃, Al₂O₃, and SiO₂ micron-powders as raw materials, CaO–Y₂O₃–Al₂O₃–SiO₂ (CYAS) glass was prepared using water cooling method. The coefficient of thermal expansion (CTE) of CYAS glass was found to be 4.3 × 10^?6/K, which was similar to that of SiC_f/SiC composites. The glass transition temperature of CYAS glass was determined to be 723.1 °C. With the increase of temperature, CYAS glass powder exhibited crystallization and sintering behaviors. Below 1300 °C, yttrium disilicate, mullite and cristobalite crystals gradually precipitated out. However, above 1300 °C, the crystals started diminishing, eventually disappearing after heat treatment at 1400 °C. CYAS glass powder was used to join SiC_f/SiC composites. The results showed that the joint gradually densified as brazing temperature increased, while the phase in the interlayer was consistent with that of glass powder heated at the same temperature. The holding time had little effect on phase composition of the joint, while longer holding time was more beneficial to the elimination of residual bubbles in the interlayer and promoted the infiltration of glass solder into SiC_f/SiC composites. The joint brazed at 1400 °C/30 min was dense and defect-free with the highest shear strength of about 57.1 MPa.     

Inhibition of abnormal grain growth in BaTiO3 by addition of Al2O3

The effect of additions of up to 1 mol% Al₂O₃ on abnormal grain growth in BaTiO₃ samples sintered at 1200 and 1250 °C has been studied. Samples with and without additions of 0.4 mol% TiO₂ were prepared. For the samples without added TiO₂, addition of 0.1 mol% Al₂O₃ increases the number density of abnormal grains, with further additions reducing the number density. The initial increase in number density is caused by Al₂O₃ forming a solid solution with BaTiO₃ and releasing TiO₂ to the grain boundaries. This excess TiO₂ then reacts with BaTiO₃ to form Ba₆Ti₁₇O₄₀, which promotes {1 1 1} twin formation and abnormal grain growth. Further additions of Al₂O₃ react with BaTiO₃, Ba₆Ti₁₇O₄₀ and excess TiO₂ to form Ba₄Al₂Ti₁₀O₂₇ and BaAl₂O₄ second phases, neither of which are growth sites for abnormal grains. For the samples with added TiO₂, addition of Al₂O₃ decreases the number of abnormal grains due to the Al₂O₃ reacting with the excess TiO₂ and BaTiO₃ to form Ba₄Al₂Ti₁₀O₂₇ and BaAl₂O₄ instead of Ba₆Ti₁₇O₄₀.