THE HIGH-TEMPERATURE THERMAL-EXPANSION OF BIPBSRCACUO SUPERCONDUCTOR AND THE OXIDE COMPONENTS (BI2O3, PBO, CAO, CUO)

The thermal expansion of superconducting Bi1.6Pb0.4Sr2Ca2Cu3Ox (BiPbSr CaCuO) and its oxide components Bi2O3, PbO, CaO and CuO have been stud ied by high-temperature dilatometric measurements (30-800 degrees C). The thermal expansion coefficient for the BiPbSrCaCuO superconductor i n the range 150-830 degrees C is alpha = 6.4 x 10(-6) K-1. The tempera ture dependences of Delta L/L of pressed Bi2O3 reveals sharp changes o f length on heating (T-1 = 712 degrees C), and on cooling (T-2 = 637 d egrees C and T-3 = 577 degrees C), caused by the phase transition mono clinic-cubic (T-1) and by reverse transitions via a metastable phase ( T-2 and T-3). By thermal expansion measurements of melted Bi2O3 it is shown that hysteresis in the forward and the reverse phase transitions may be partly caused by grain boundary effect in pressed Bi2O3. The t hermal expansion of red PbO reveals a sharp decrease in Delta L/L on h eating (T-1 = 490 degrees C), related with the phase transition of tet ragonal (red, a = 0.3962 nm, c = 0.5025 nm) - orthorhombic (yellow, a = 0.5489 nm, b = 0.4756 nm, c = 0.5895 nm). The possible causes of irr eversibility of the phase transition in PbO are discussed. In the rang e 50-740 degrees C the coefficient of thermal expansion of pressed Bi2 O3 (alpha(m) = 3.6 x 10(-6) and alpha(c) = 16.6 x 10(-6) K-1 for monoc linic and cubic Bi2O3 respectively), the melted Bi2O3 (alpha(m) = 7.6 x 10(-6) and alpha(c) = 11.5 x 10(-6) K-1), PbO (alpha(t) = 9.4 x 10(- 6) and alpha(or) = 3.3 x 10(-6) K-1 for tetragonal and orthorhombic Pb O respectively), CaO (alpha = 6.1 x 10(-6) K-1) and CuO (alpha = 4.3 x 10(-6) K-1) are presented.