Tatsuya Shirakami

Effects of heat treatment on the phase transitions in BaTiO3 fine particles

Abstract Effects of heat treatment were investigated on the phase transitions in BaTiO3 fine particles synthesized by hydrothermal method. The virgin fine particles and the samples treated below 400°C showed no phase transition below room temperature, while the intrinsic successive phase transitions were detected for the samples treated above 600°C by the low temperature heat capacity measurements. The enthalpy and entropy of the orthorhombic-tetragonal phase transition increased with increasing temperature of heat treatment and approached to the values of the bulk sample obtained by melt-frozen method.

Spin glass-like magnetic properties of LiNiO2

Very near stoichiometric compound of Li 1- x Ni 1+x O 2 (x 0.01) was synthesized by a new process at a reaction temperature of 650°C. The DC and AC magnetic susceptibility of the sample was measured using a SQUID magnetometer, and a typical spin glass-like behavior was observed. The zero field cooled susceptibility showed a cusp-like peak at 8 K. On the other hand, the field cooled susceptibility showed little temperature dependence below 8 K. The AC susceptibility has a maximum around 8-9 K, of which the temperature varied with the frequency.

Crystal structure of a new oxide, Nd2TiMnO6

Abstract A new ternary compound, Nd 2 TiMnO 6 , was synthesized in a reducing atmosphere at 1523 K. The lattice constants and space group of Nd 2 TiMnO 6 were determined by powder X-ray diffraction (XRD) and electron diffraction (ED) methods, with the aid of high-resolution electron microscopy (HRTEM). The crystal has an orthorhombic unit cell with space group Pnma (No. 62) and cell dimensions a = 0.57145(3), b = 0.78589(6), and c = 0.55002(3) nm.

A New Method of Determining Short-Range Order Parameter in Relaxor Pb(Ni1/3Nb2/3)O3 by Magnetic Susceptibility Measurement.

We synthesized Pb(Ni1/3Nb2/3)O3 (PNN) and performed selected-area electron diffraction (SAD) in order to investigate the structure of the B-site array. In addition to the reflection from the basic cell, the SAD pattern of sintered PNN corresponds to the reciprocal plane normal to the [011] zone axis and showed diffuse scatterings at (½½½) positions. We also measured the magnetic susceptibility of PNN and discussed the short-range ordering around Ni2+ ions by analyzing the susceptibility based on a simple model.

Magnetic properties of Eu2MnxZr2−xO7−δ

Abstract Compounds formed in the ternary system, MnO–Eu 2 O 3 –ZrO 2 , have been prepared from starting mixtures with a formula, Eu 2 Mn x Zr (2− x ) O 7− δ , by firing at 1623 K in a reducing atmosphere. Those compounds are solid solutions of a pyrochlore type and a rare earth type. The former occurs in the region of x being less than 0.65 and the latter appears in the region x being larger than 0.7. Solubility of manganese ions in those solid solutions has been measured by EPMA and the maximum value reaches about 1.8%. Magnetic properties of the solid solutions indicate that little amount of manganese ions is incorporated in the solid solutions.

Pressure induced mosaic structure of barium titanate and its heat capacity

Barium titanate powder was cold isostatic pressed (CIPed) up to 1.0 GPa in order to investigate effects of pressure on ferroelectric transformations. Crystallite size and lattice strain of CIPed powders were evaluated. Heat capacities ranging from 13 to 420 K were measured. Further, mosaic structures of CIPed powders were revealed by TEM. Transformation temperatures were almost independent of crystallite size from 84 nm (non CIPed) down to 61 nm (1.0 GPa). However, the enthalpy of ferroelectric transformation of the CIPed was only 6.7% of that of the starting material.

Electron microscopy study of a manganese-doped holmium zirconium oxide solid solution

Abstract A new material, manganese-doped holmium zirconium oxide solid solution, was synthesized in a reducing atmosphere at 1623 K. Microstructural characterization of the material was performed using transmission electron microscopy (TEM) in conjunction with energy-dispersive X-ray spectroscopy (EDXS). It was confirmed that the material consisted of two phases having a similar basic cell related to the fluorite-type structure. One of the phases builds up the matrix and reveals the fluorite-type structure. The other phase has a structural modulation along the direction of the basic cell, with spacing two times that of the (110) plane, and occurs as small precipitates, 70–100 nm in size, embedded in the matrix. A lattice correspondence was maintained between the precipitates and the matrix with a small strain. The holmium content in the precipitates is higher than that of the matrix, which gives rise to the structure modulation along the direction.