Key Engineering Materials Vol. 388

Abstract: The factor determining texture development was examined for Bi0.5Na0.5TiO3 ceramics made by the reactive-templated grain growth process using platelike Bi4Ti3O12 particles as reactive template. Platelike, skeleton Bi0.5Na0.5TiO3 particles were formed by the reaction between Bi4Ti3O12 and Na2CO3 in calcined compacts. Coalescence of small grains in the skeleton particles to form single template particles was important to obtain highly textured ceramics.

Abstract: Mn-doped Na0.5K0.5NbO3 (NKN) crystals have been grown by self-flux method under several heat-treatment conditions. The cooling rate affected the quality of Mn-doped NKN crystals significantly. When the cooling rate was 0.5 oC/min at temperatures ranging from 1050 to 950 oC, the synthesized Mn-doped NKN crystal exhibited a single nucleation growth, compared with multinucleation growth when the cooling rate was 0.25 oC/min at temperatures ranging from 1050 to 950 oC. The frequency dependence on the ferroelectric P-E hysteresis loop of the Mn-doped NKN crystal was not observed at measurement frequency of 0.1 – 25 Hz. The annealed 0.5 mol% Mn-doped NKN crystal exhibited excellent P-E hysteresis loop with Pr of 45.0 μC/cm2 and Ec of 7.2 kV/cm.

Abstract: Poly- and single-crystalline BaTi2O5 co-substituted with SrO and ZrO2, Ba0.99Sr0.01(Ti1-xZrx)2O5 (BT2SZ) were prepared by arc-melting and floating-zone (FZ) melting, respectively. The specimens showed a significant (020) orientation. The highest permittivity of poly-crystalline BT2SZ was 3880 at x = 0.005 and that of single-crystal was 27000 at x = 0.005. The Curie temperature (Tc) of poly-crystals decreased from 750 to 640 K with increasing x from 0 to 0.026 and that of single-crystals decreased from 750 to 710 K with increasing x from 0 to 0.008. The highest remnant polarization of single crystalline BT2SZ was 7.8×10-2 Cm-2 at x = 0.008, higher than that of the poly-crystal.

Abstract: The electrooptic material of transparent (Sr,Ba)Nb2O6 (SBN) ceramics was prepared using the conventional solid-phase reaction process with no special techniques such as hot-pressing or hot isostatic pressing. The SBN ceramics were made transparent by substituting a small amount of Zn2+ ion for the B site (Nb5+ ion site). The Curie temperature was increased by substituting a small amount of Na+ ion for the A site (Sr2+ or Ba2+ site). Furthermore, the orientation of the SBN structure by the template grain growth (TGG) method improved the electrooptic properties of the ceramics.

Abstract: A conventional solid phase reaction method was followed to prepare (1−x)BaTiO3-xCaTiO3 based ceramics with content fractions ranging from x = 0.00 to 1.00. Phase segregation was observed when x exceeded 0.10. DC breakdown voltage (DC-BDV) abruptly changed at x = 0.30 and 0.85. Furthermore, the DC-BDV values of insoluble compositions (x = 0.30−0.85) were much higher than those of solubility limit (x = 0.20 and 0.90). Results obtained by investigation of the amount of absorbed current and the dependence of the rate of voltage increase for DC-BDV and AC-BDV confirmed the formation of space charge in insoluble compositions. This suggests that the dependence of the DC-BDV value for (1−x)BaTiO3-xCaTiO3 based ceramics was affected by the formation of space charge.

Abstract: (1-x)(Bi1/2Na1/2)TiO3-xBiAlO3 [BNTA100x (0 ≤ x ≤ 0.14)] ceramics were prepared by a conventional ceramic fabrication process. Single-phase perovskite structures were formed when x ≤ 0.08 for BNTA100x. The depolarization temperature, Td, at which piezoelectricity disappears, decreased with increasing x. The piezoelectric constant, d33, increased with increasing x because of the increase in free permittivity accompanied with decreasing Td. d33 and the electromechanical coupling factor, k33, of BNTA6 were 93 pC/N and 0.41, respectively. Normalized strain d33* (= Smax/Emax) at 60 kV/cm at the maximum field-induced strain was 122.2 pm/V for BNTA8. The value of d33* was higher than the calculated value of d33.

Abstract: Piezoelectric and dielectric properties of (LixNa1-x)NbO3 (LNN100x; x≤0.14) ceramics were investigated according to phase transition The highest electromechanical coupling factor, kp, of 0.247 was obtained for LNN12 which has a composition with a morphotropic phase boundary at room temperature. On the other hand, the coupling factor of k33 with longitudinal mode was almost constant for all compositions of x. The dielectric constant, ε r, before poling treatment exhibited a thermal hysteresis near the Curie temperature, TC, for all compositions. The depolarization temperature of LNN6 was higher than the TC before poling treatment. In addition, the peak of free permittivity, ε33 T, was shifted to higher temperature. It was considered that the phase transition was induced by the electric field during poling treatment.

Abstract: Superlattice-structured Bi4Ti3O12- PbBi4Ti4O15 single crystals were grown, and their properties of polarization hysteresis and leakage current along the a axis were investigated. Oxidation annealing led to a marked increase in leakage current, while annealing in N2 atmosphere yielded a marked decrease in leakage current at room temperature. These results show that electron hole is the dominant carrier for the leakage current. A well-saturated polarization hysteresis with a remanent polarization of 41 μC/cm2 was observed, which is suggested to originate from the peculiar ferroelectric displacement of Bi in the Bi2O2 layers.

Abstract: 0.999Bi0.5Na0.5TiO3-0.001BaTiO3 (BNT-0.1%BT) single crystals with a maximum size of 1×1×1 mm3 were successfully grown by a flux method using BNT-6%BT powder and Bi2O3 as a flux. The crystals showed a remanent polarization of 33 μC/cm2 and coercive electric field of 40 kV/cm along [100]Cubic. Electric-field induced strain measurements along [100]Cubic revealed an effective piezoelectric strain constant d33 * of 80 pm/V.

Abstract: Ba(Mg1/3Ta2/3)O3 (BMT) powders were successfully prepared by ultrasonic spray pyrolysis from an aqueous solution of Ba, Mg and Ta. The particles characteristics of BMT nano-sized powders were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). As-prepared powder particles had a sub-micrometer size with a narrow distribution. Transmission electron microscopy (TEM) observation revealed that the average size of the BMT nano-particles was around 20 nm, and that these particles were aggregated. The dielectric constant (r) of 23.2 and the Q・f of 98,300 were obtained at 1550°C by a spray pyrolysis.