X-Ray Study of the Structure and Thermal Properties of Ba1–xKxBiO3 at Different Temperatures

The crystal structure as well as the temperature and composition dependences of the lattice parameters, the thermal expansion coefficients in the high-temperature superconducting Ba_1–xBiO₃ system were determined by an X-ray powder diffraction method at temperatures between 80 and 650 K. The character of variation of intensity, profiles, and line widths of the diffraction lines for different perovskite structures as a function of the content x and temperatures was found. The correlation between the behaviour of the thermal expansion coefficients and potassium content was revealed at different temperatures. It is shown that the thermal expansion coefficients vary inversely with rising x at any temperature in the range from 80 to 400 K.