Key Engineering Materials Vol. 485

Abstract: The structural, and dielectric and piezoelectric properties of (1-x)BaTiO3 – x Bi_1/2K_1/2(X_1/3Nb_2/3)O₃ (X=Cu, X=Mg or X=Zn) ceramic were studied. The single perovskite phase was observed when x≤0.5 for X=Cu and Mg and x≤0.2 for X=Zn. As x increased, the dielectric constant peak temperature and piezoelectric properties continuously decreased for X=Mg and Zn. On the other hand, those of X=Cu possessed a local maxima at x=0.7 and the peak temperature was 200°C and the large field piezoelectric constant, d₃₃*, was 94 pC/N.

Abstract: High-power piezoelectric characteristics of (Bi_1/2Na_1/2)TiO₃ (BNT)- and KNbO₃ (KN)-based ceramics at continuous driving were investigated. The selected compositions of BNT- and KN-based ceramics were 0.88(Bi_1/2Na_1/2)TiO₃-0.04(Bi_1/2Li_1/2)TiO₃-0.08(Bi_1/2K_1/2)TiO₃ doped with 0.6 wt% MnCO₃ [BNLKT4-8Mn0.6] and KNbO₃-MnCO₃ 0.8 wt% [KN-Mn0.8] ceramics. It was found that the vibration velocity v_0-P of BNLKT4-8Mn0.6 and KN-Mn0.8 ceramics linearly increased up to approximately 0.8 and 0.6 m/s, respectively. The temperature increases of BNLKT4-8Mn0.6 and KN-Mn0.8 ceramics were approximately 5°C under continuous driving at the vibration velocity of 0.6 m/s.

Abstract: Effect of the microstructural homogeneity of 0.5 BaTiO₃ - 0.5 KNbO₃ (0.5BT-0.5KN) solid solution ceramics on the dielectric and piezoelectric properties was investigated. Microstructure of a sample prepared by a conventional sintering method was homogenous, and the room temperature crystal structure was assigned to cubic Pm3m symmetry and therefore the sample was paraelectric. On the other hand, microstructure of samples prepared by a two-step sintering method was inhomogeneous, that is, it was made of BT and KN grains. The large electric field piezoelectric constant d₃₃* increased with increasing interface area.

Abstract: The high-power piezoelectric characteristics of lead-free piezoelectric ceramics, based on a bismuth layer-structured ferroelectric, MnCO₃-doped (Sr_0.7Ca_0.3)₂Bi₄Ti₅O₁₈ (abbreviated as SCBT0.3 + Mn x wt%), were studied. SCBT0.3 + Mn x wt% lead-free ceramics showed an extremely high mechanical quality factor (Q_m) of more than 3000 in the (33) vibration mode under small-amplitude vibration. The high-power piezoelectric characteristics of SCBT0.3 + Mn x wt% were measured using the high-power measurement method based on frequency sweep driving under a constant voltage condition. It was found that the vibration velocity v_0-p of SCBT0.3 + Mn 0.2 wt% linearly increased up to approximately 3.0 m/s. Therefore, the Mn-doped SCBT0.3-based ceramics are a promising candidate for lead-free high-power applications.

Abstract: We have successfully synthesized single-crystal samples of fast Li-ion conducting cubic Li₇La₃Zr₂O₁₂ with the garnet related-type structure by a self-flux method using LiNO₃ at 1150°C. The as-grown Li₇La₃Zr₂O₁₂ crystals are colorless and transparent; they also have a polyhedral-shape with a maximum dimension of 0.15 ´ 0.10 ´ 0.10 mm³. The powder XRD pattern shows the obtained crystals have cubic Li₇La₃Zr₂O₁₂ structure, and the EDX analysis confirms the chemical composition of La : Zr = 3 : 2.

Abstract: Lithium intercalation properties of lithium tetratitanate obtained by nanosheets process (NS-LT4) was examined and compared with those of conventional lithium tetratitanate. NS-LT4 was prepared by restacking of tetratitanate nanosheets with LiOH aqueous solution. NS-LT4 exhibited a reversible capacity of approximately 140 mAh g^-1, which corresponds to approximately two Li insertions per formula unit. Two Li insertions per formula unit mean that half of the Ti atoms were reduced from a tetravalent state to a trivalent state. The quasi open-circuit voltage of NS-LT4 was comparable with that of conventional lithium tetratitanate, and the voltage change of NS-LT4 as the change in lithium composition was greater than that of conventional lithium tetratitanate. This potential behavior would be caused by the unique stacking structure with stacking fault and random rotation in nanosheet-plane generated during the restacking of nanosheets.

Abstract: Spherical LiFePO₄/C precursor powders were successfully prepared by spray pyrolysis. Various types of organic compounds such as glycolic acid, malic acid, citric acid, fructose and sucrose were used as carbon sources. X-ray diffraction analysis revealed that the olivine phase was obtained by calcining over 600 °C under an argon (95%)/hydrogen (5%) atmosphere. The particles exhibited a spherical morphology with approximately 1.5 μm. LiFePO₄/C cathode derived from sucrose exhibited higher rechargeable capacity and cycle stability. The rechargeable capacity of LiFePO₄/C cathode was approximately 154 mAh/g at 1 C. 90% of initial discharge capacity was maintained after 100 cycles.

Abstract: Al doped LiMn₂O₄ powders were prepared by spray pyrolysis using the aqueous solution of manganese carbonate. The aqueous solution, in which manganese carbonate was uniformly dispersed by a surfactant, was used as the starting solution. Al₂O₃ nanopowders, Al(OH)₃ and Al(NO₃)₃·9H₂O were used as the doping agent of Al. A scanning electron microscope photograph showed that Al doped LiMn₂O₄ powders had spherical morphology with broad particle size distribution. X-ray diffraction revealed that crystal phase of all samples were good agreement with spinel phase. The rechargeable capacity of Al doped LiMn₂O₄ cathode was about 110 mAh/g at 1 C regardless of doping agent. 75% of initial discharge capacity was maintained after 100 cycles

Abstract: C/LiMnPO₄ materials were synthesized by the complex polymerized method. An orthorhombic olivine type structure was obtained by calcination at temperatures over 973 K under an argon/hydrogen (5%) atmosphere. Differential thermogravimetric analysis showed that the carbon content of C/LiMnPO₄ was about 65 wt%. The initial discharge capacity of C/LiMnPO₄ calcined at 973 K was 135 mAh/g at 0.1 C and 60 mAh/g at 1 C.

Abstract: Li₄Ti₅O₁₂ powders were synthesized by solid state reaction of Li₂CO₃ and spherical composite powders of carbon and TiO₂ (denoted as C/TiO₂). C/TiO₂ powders were synthesized by spray pyrolysis of using lactic acid aqueous solution. The particle characteristics of Li₄Ti₅O₁₂ powders were determined by SEM, XRD and DTA-TG. DTA-TG showed that the carbon content was around 8 wt% in Li₄Ti₅O₁₂ powders. XRD revealed that the spinel structure (Fd3m) was obtained by heating at 750 °C under N₂ atmosphere. The first rechargeable capacity of Li₄Ti₅O₁₂ anode was about 160 mAh/g at 1 C. That of Li₄Ti₅O₁₂ anode decreased to 90 mAh/g at 20 C. The rechargeable capacity of Li₄Ti₅O₁₂ anode decreased with increasing the rechargeable rate, but 81% of initial discharge capacity of Li₄Ti₅O₁₂ anode was retained after 200 cycles at 1C