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)

Abstract

A simple, rapid, and inexpensive heating‐wire technique is used for physical observations at high temperatures. The upper limit is 2000 K in air with platinum‐iridium or platinum‐rhodium wires and 2700 K with iridium;temperatures up to 3600 K can be achieved under an inert atmosphere with tungsten wires. Raman spectroscopymeasurements made up to 1900 K by this technique suggest that the high‐temperature harmonic vibrational behavior of corundum (α‐Al2O3) results from the cancellation of anharmonic effects. Powder x‐ray diffraction experiments with synchrotron radiation show that perovskite (CaTiO3) changes from orthorhombic symmetry to cubic between 1330 and 1530 K, with an intermediate tetragonal phase likely, consistent with λ‐type transitions recorded by recent calorimetric measurements. Finally, observations of CaAl2Si2O8polymorphism has shown the existence of a new metastable phase.