Orthorhombic-tetragonal Phase Boundary Research Articles

Crystalline structural phase boundaries in (K,Na,Li)NbO 3 ceramics

Lead-free (K x Na 1− x ) 1− y Li y NbO 3 ceramics (with x = 0.50 , y = 0 – 0.08 and x = 0.30 – 0.70 , y = 0.06 , respectively) were synthesized using the conventional solid-state reaction technique. Compositional influences of K, Na and Li constituents on microstructures, crystalline structures, dielectric and piezoelectric properties were investigated. It has been known that microstructures change largely with the alkali constituents and that there exist three orthorhombic-tetragonal phase boundaries at room temperature. One occurs in (K 0.50Na 0.50) 1− y Li y NbO 3 ceramics at y = 0.05 – 0.06 , which corresponds to the previously reported morphotropic phase boundary (MPB). The other two appear in (K x Na 1− x ) 0.94Li 0.06NbO 3 ceramics near x = 0.40 and x = 0.60 , respectively. (K 0.50Na 0.50) 0.935Li 0.065NbO 3 and (K 0.45Na 0.55) 0.94Li 0.06NbO 3 ceramics show high piezoelectric properties with the d 33 values over 200 pC/N and the k p values around 45% at room temperature. It is thought that the observed high piezoelectric properties are largely affected by the temperature-driven orthorhombic-tetragonal phase transition.

Effect of oxygen deficiency on the thermal expansion of high Tc superconductor YBa 2Cu 3O 7-Δ

Thermal expansion coefficients of the high- T c superconductor YBa 2Cu 3O 7-δ have been measured for δ=0.15, 0.40, 0.70 and 0.9 in the temperature range from 5 to 200 K. There is no anomaly in the α( T) curve near the superconducting transition temperature T c. It is found that the values of α/ T(10 K) have a maximum near the orthorhombic-tetragonal phase boundary, δ ≈ 0.8. The origin of the anomaly is discussed in connection with the structural disorder and the antiferromagnetism.

High pressure studies of high T c superconductor YBa 2Cu 3O 7−δ

The effect of pressure on the electrical resistance, the lattice constant and the crystal structure of YBa 2Cu 3O 7−δ (YBCO) have been studied at high pressure in the wide range of δ. It is found that the compressibility of superconducting YBCO increases with δ, having a peak near the orthorhombic-tetragonal phase boundary δ ≅ 0.8. T c increases with pressure, at a rate 0.09 K/kbar.

Effect of Oxygen Deficiency on the Compressibility of High-TcSuperconductor YBa2Cu3O7-δ

The effect of pressure on the lattice constant and crystal structure of YBa 2 Cu 3 O 7-δ (YBCO) has been studied up to about 120 kbar at room temperature in the wide range of δ, 0<δ<1. It is found that the lattice compression of all samples is anisotropic, and the volume compressibility of superconducting YBCO increases with δ, having a peak near the orthorhombic-tetragonal phase boundary δ≃0.8.