RAMAN-SPECTROSCOPY, X-RAY-DIFFRACTION, AND PHASE RELATIONSHIP DETERMINATIONS WITH A VERSATILE HEATING CELL FOR MEASUREMENTS UP TO 3600-K (OR 2700-K IN AIR)

A simple, rapid, and inexpensive heating-wire technique is used for ph ysical observations at high temperatures. The upper limit is 2000 K in air with platinum-iridium or platinum-rhodium wires and 2700 K with i ridium; temperatures up to 3600 K can be achieved under an inert atmos phere with tungsten wires. Raman spectroscopy measurements made up to 1900 K by this technique suggest that the high-temperature harmonic vi brational behavior of corundum (alpha-Al2O3) results from the cancella tion of anharmonic effects. Powder x-ray diffraction experiments with synchrotron radiation show that perovskite (CaTiO3) changes from ortho rhombic symmetry to cubic between 1330 and 1530 K, with an intermediat e tetragonal phase likely, consistent with lambda-type transitions rec orded by recent calorimetric measurements. Finally, observations of Ca Al2Si2O8 polymorphism has shown the existence of a new metastable phas e.