P. Kantha

Microstructure and electrical properties of BaFe 0.5Nb 0.5O 3 Doped with GeO 2 (1-5 wt.%)

In this work, the effects of GeO2 dopant on the electrical properties of BaFe0.5Nb0.5O3 (BFN) perovskite ceramics were investigated. The BFN powder was prepared by a conventional mixed-oxide method using stoichiometric amounts of BaCO3, Fe2O3 and Nb2O5. Afterward the GeO2 contents, ranging from 1 to 5 wt.%, were added to the calcined BFN powder and mixed via vibro-milling method. The mixtures were pressed and sintered at 1125–1150°C for 4 h to form dense ceramics. We showed that the addition of GeO2 caused a reduction of grain size and formation of secondary phases: Ba3Fe2Ge4O14 and BaGeO3. The maximum densities of these BFN doped with GeO2 ceramics were slightly lower than those of the pure BFN due to the occurrence of pores. We also found that the GeO2 doping could improve the dielectric properties of these ceramics at room temperature (25°C). The 1 wt.% GeO2 doped sample exhibited higher dielectric constant of about 1800 and lower dielectric loss of 0.45 comparing to that of pure BFN. However, the dielectric constant values of these ceramics at high temperature (>25°C) were decreased significantly with the increase of GeO2 concentration. In addition, the GeO2 additive gave a weak ferroelectric behavior, leading to change in the pyroelectric coefficient and spontaneous polarization of the GeO2 doped BFN ceramics.

Dielectric properties of lead-free solid solution of Bi0.487Na0.487La0.017TiO3 and BaTiO3

Bismuth sodium titanate (Bi0.5Na0.5TiO3; BNT) is one of the most preferred materials for the preparation of lead-free ceramics; however its dielectric property is lower than that of lead-based materials. Thus, the substitution of A and B-site cations is considered to be one of the best solutions in order to improve both the dielectric and piezoelectric properties. In this study, lead-free ceramics from bismuth sodium lanthanum titanate (Bi0.487Na0.487La0.017TiO3; BNLT) and barium titanate (BaTiO3; BT) systems were prepared by a modified two-step mixed oxide method. BT powder was added to BNLT powder with the desired compositions of (1 − x)BNLT–xBT, where x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10. It was found that the addition of BT in the BNLT improved the electrical properties of ceramics. Phase transition of rhombohedral to tetragonal structure was significantly dependent on the amount of BT added. It was also found that the change in crystal structure affected the ferroelectric property of the ceramics where the transition from ferroelectric to antiferroelectric started from the samples with x ≥ 0.06 mol% and higher. This may be useful in terms of using these materials in the desired applications.

Effect of BaZr0.05Ti0.95O3 Addition on Microstructure and Piezoelectric Properties of Hydroxyapatite Bone

The aim of this study was to investigate the effect of BaZr0.05Ti0.95O3 (BZT) addition on the microstructure, physical, dielectric and piezoelectric properties of hydroxyapatite (HA), and develop new biomaterials which have potential applications in the support for cellular growth and in the system for bone regeneration. In this case the BaZr0.05Ti0.95O3- HA composites (HABZT) were prepared by conventional sintering method. The BZT were added to HA with ratio 0, 10, 20 and 30 %wt. Then the mixed powders were pressed and subsequently sintered at the temperature ranging from 1150 to 1350°C. The result showed that the dielectric and piezoelectric properties were improved by the addition of BZT. Moreover, the bioactivity of the HA improved with addition of BZT especially at 10% as evident by the formation of bone like apatite layers on the surface of all BCZT composites after soaking in simulated body fluid (SBF) for 15 days. The results confirmed the possibility of using these bioactive composites for treatment within the human body.

Enhanced electrical properties of lead-free Bi2GeO5 ferroelectric glass ceramics by thermal annealing

To study the effect of thermal annealing on the electrical properties of lead-free Bi2GeO5 ferroelectric glass ceramics, the glass ceramics with composition of Bi2GeO5 were prepared by the conventional melt-quenching and heat-treatment methods subsequently. Glass ceramics of Bi2GeO5 was produced by subjecting the glasses from BiO1.5-GeO2-BO1.5 system to the heat treatment schedule at 475°C for 18 h. After that, the resulting samples were separately annealed at 275 and 375°C for 4, 8, 12 and 18 h, respectively. The important properties of the annealed Bi2GeO5 glass ceramics such as physical properties, phase formation and electrical properties were then investigated. It was found that the annealing treatment played an important role on electrical properties of these glass ceramics. The XRD patterns confirm the secondary phase of Bi4Ge3O12 co-existed with Bi2GeO5 which increased at higher annealing temperature and time. This caused a change in density and related electrical properties of the Bi2GeO5 glass ceramics. Both annealing temperature of 275 and 375°C with various times can improve dielectric properties and ferroelectric behavior of the resulting Bi2GeO5 glass ceramics when comparing with that of un-annealed sample. The optimum annealing temperature and time for the improvement of dielectric properties of Bi2GeO5 glass ceramics was found at 375°C/12 h, where the maximum values of the dielectric constant (ϵr) of 246 and low dielectric loss (tanδ) of 0.024 were obtained. Moreover, the ferroelectric property of all annealed glass ceramics exhibited the slim P-E loop and Pr values which slightly increased with increasing annealing temperature and time. However, the P-E loops are not the feature of truly ferroelectric, it may be represent a lossy capacitor behavior.

Effect of Heat Treatment Conditions on Properties of Lead‐Free Bi2GeO5 Ferroelectric Glass Ceramics

Nowadays, lead‐free ferroelectric materials have attracted much interest among materials scientists as a result of environmental concern. The bismuth germanate (Bi2GeO5) phase, one of the lead‐free ferroelectric crystals, is of particular interest as its composition already contains good glass former (GeO2) and can be prepared by an alternative glass ceramic route. In this work, the conventional melt‐quenching method was used to produce the parent glass with composition of 60 mol% BiO1.5:20 mol% GeO2:20 mol% BO1.5. The as‐received glass pieces were subjected to the heat treatment schedule at various crystallization temperatures and dwell‐times. The glass and glass ceramics samples were then investigated by XRD, Raman spectroscopy and their dielectric properties were also measured. The XRD and Raman spectroscopy showed that the crystallinity of the prepared glass ceramics depended very much on crystallization temperature and dwell‐time. The larger dielectric constant and lower dielectric loss were obtained...

The influence of heat treatment condition on electrical properties of glass-ceramics containing ferroelectric lead bismuth germanate ((Pb 3Bi2(GeO4)3)

Glasses have been formed from PbO-Bi3O2-GeO2 system by conventional melt-quenching method. The glasses were melted in Pt crucible in an air atmosphere. The resulting glass pieces were subjected to the heat treatment schedule at various crystallization temperatures. The glass and glass-ceramics samples were then investigated by XRD and SEM spectroscopy. The dielectric and ferroelectric properties were also measured. Moreover, DTA analysis has been used to examine the crystallization temperatures of glasses. The controlled heat treatment process has been applied to the crystallization temperatures and glass-ceramic samples were obtained. The XRD showed that the crystals of ferroelectric phase, hexagonal Pb3Bi2(GeO4)3;PBG, were precipitated in the glass matrix and this is the dominant phase in the region of 34.50 mol% PbO : 11.49 mol% Bi2O3 : 54.01 mol% GeO2 on the heat treatment temperature at 527°C. The dielectric constant (ϵr) and P-E loop of Pb3Bi2(GeO4)3 glass-ceramic confirmed that this material may have high possibility to be ferroelectric at room temperature with coercive field (Ec) of 30.9 kV/cm. However, the remanent polarization (Pr) = 1.36 μC/cm2 is rather small, therefore it is quite difficult to confirm that the P-E loop is the feature of truly ferroelectric, it may represent a lossy capacitor behavior.

The Effect of Processing Parameters on Properties of Bi2GeO5 Glass Ceramics

In this research, it is interesting to fabricate glass ceramics containing lead free ferroelectric crystals. The new lead free ferroelectric phase of interest is orthorhombic Bi2GeO5 which are precipitated in the BiO1.5-GeO2-BO1.5 system and studied in the region of 60 mol% BiO1.5:20 mol% GeO2: 20 mol% BO1.5. The glasses were prepared by conventional melt-quenching method. The glasses were melted separately in Pt and Al2O3 crucible in an air atmosphere. It is found that the as-received glasses were easily obtained from Al2O3 crucible while that from Pt crucible devitrification of Bi2GeO5 crystals were observed in some glasses, giving rise to an instability and difficulty in obtaining good based glasses by using this Pt crucible. The glass ceramics prepared from Pt crucible crystallized into two phases of the expected Bi2GeO5 and second phase Bi4Ge3O12 while Bi2GeO5 phase only observed in the glass ceramics prepared from Al2O3 crucible. Crystallinity and phases of the glass ceramics have a significant effect on their dielectric properties.

Dielectric Relaxation and Electrical Properties of Lead-Free Perovskite BaGex(Fe0.5Nb0.5)1−xO3 Ceramic

The lead-free BaGex(Fe0.5Nb0.5)1−xO3: BGFN ceramics were synthesized by a solid state reaction technique. The BGFN powders were produced via mixed-oxide method with the desired compositions of BaGex(Fe0.5Nb0.5)1-xO3 where x = 0.01, 0.015, 0.02 and 0.025, respectively and subsequently calcined at different temperatures from 1100 to 1200°C for 4 h. The mixtures were pressed in to pellets and sintered at 1200 to 1350°C for 4 h to form dense ceramics. The characteristics, including phase formation, microstructures, dielectric properties and pyroelectric properties were also investigated. It was observed that the Ge4+ cations played an important role on the change of crystal structures and the phase formation of the BGFN phases. The XRD results indicated that the structure of BFN is cubic and transforms to monoclinic when the Ge concentration is over 0.015. Moreover, the higher level of Ge4+ addition caused a reduction of grain size and formation of secondary phases: Ba3Fe2Ge4O14 and BaGeO3. The amount of each phase was depended on the concentration of Ge where the Ba3Fe2Ge4O14 and BaGeO3 phases were found to increase with increasing of x content. This in turn affected their electrical properties where dielectric constant (ϵr) was dominately decreased while the dielectric loss and the pyroelectric properties were greatly improved. The optimum composition for this system was found to be x = 0.01, where the maximum values of dielectric constant (∼12000) with relatively lower dielectric loss (0.95) at 1 KHz and at room temperature were achieved. The change in the pyroelectric coefficient and spontaneous polarization of the BFN ceramic is possibly due to the segregation of Ge4+ at grain boundary, resulting in resistance to domain switching during heating or cooling the sample. This promises a good candidate for the new lead free ceramic for applications in capacitors.

Microstructure and dielectric properties of bismuth germanate glass-ceramics

Bismuth germanate composites containing Bi2GeO5-Bi4Ge3O12 phases were prepared by glass ceramic method and sintering techniques. The existences of three bismuth germanate crystals of Bi2GeO5, Bi4Ge3O12 and BiBO3 were found in XRD patterns. The amount of each phase depended mostly on the sintering temperature where the Bi4Ge3O12 phase was found to increase with increasing sintering temperature. The mixing of round and pyramidal shape crystals was observed in the sample sintered at 650°C. This gave rise to the improvement in its dielectric properties where the ϵr was found to increase from ∼78 to ∼395 for the sample sintered at 500°C and 650°C, respectively. Moreover, the tanδ was found to decrease greatly with increasing sintering temperature. Thus, this Bi2GeO5-Bi4Ge3O12 composite may be considered as a promising candidate of microwave dielectric materials.

Influence of germanium substitution on dielectric and ferroelectric properties of Ba(Fe 0.5 Nb 0.5 )O 3 ceramics

In this work, the influence of Ge⁴⁺ substitution on dielectric and ferroelectric properties of high dielectric BaFe_0.5Nb_0.5O₃ ceramics was studied. The BGFN powders with a formula BaGe_x(Fe_0.5Nb_0.5)_1-xO₃ where x = 0.01, 0.015, 0.02 and 0.025 were produced via mixed-oxide method and subsequently calcined at 1100-1200°C for 4 h. To form the BGFN ceramics, the resulting powders were pressed into pellets and sintered at various temperatures from 1200 to 1350°C for 4 h in order to obtain the ceramic with maximum density under each condition. The phase formation, microstructure and electrical properties of these ceramics were investigated. It was found that the Ge⁴⁺ substitution played an important role on the change of crystal structures and the phase formation of the BFN ceramics. The appearance of peak shift and peak split in XRD patterns confirmed the structural change from cubic to monoclinic in the ceramic samples at higher Ge⁴⁺ content. The ceramics with x ≥ 0.015 contained three phases of BGFN, Ba₃Fe₂Ge₄O₁₄ and BaGeO₃. The amount of each phase was depended on the concentration of Ge⁴⁺ where the Ba₃Fe₂Ge₄O₁₄ and BaGeO₃ phases were found to increase with increasing x content. It was also found that the higher porosity and smaller grain sizes were found in the BGFN ceramics with higher level of Ge⁴⁺ addition. This in turn affected their dielectric properties where dielectric constant was substantially decreased while the dielectric loss was greatly improved. The optimum composition for this system was found to be x = 0.015, where the maximum dielectric constant (~12282) with lower dielectric loss at room temperature were obtained.