Investigations in High Temperature Single Crystal X-ray Crystallography

Abstract

Single crystal analysis has the advantage of giving more  detailed and significant information in several areas related to structure than the analysis of polycrystalline materials. One important investigation would be the X-ray determination of atomic vibration amplitudes over a range of temperatures up to melting point in simple structures. This would throw considerable light on the phenomenon of melting, besides providing a reliable check on the validity of the lattice dynamical models used to predict the phonon characteristics of solids. Accurate experimental data needed for such investigations call for suitable high temperature devices, which can be conveniently attached to commercially available single crystal cameras and diffractometers. Investigations in the field of high temperature single crystal X-ray diffraction were done at Physics Department, Indian Institute of Science, Bangalore during 1970–1980. Varieties of heater attachments based on resistance heating, gas flame and hot air flow technique were developed for use with commercially available single crystal X-ray cameras and diffractometers. These include heater attachments for Weissenberg camera (1000 C–3000 C), Hilger & Watts linear diffractometer (1000 C), Charles Super Co. precession camera (1000 C), a complete high temperature Weissenberg camera for single crystal data collection up to 400 C in vacuum or inert gas atmosphere and up to 900 C in air, a high temperature attachment for Enraf-Nonius CAD-4 Kappa axis diffractometer (500 C). Accurate single crystal X-ray diffraction data on NaCl, and KCl were collected on linear diffractometer from room temperature to melting point for study of thermal vibration of atoms. High temperature data with CAD-4 diffractometer was collected for study of phase transition in ferroelectric sodium metavanadate and dicalcium lead propionate, semiconductor to metal transition in Ti2O3 and Jahn Teller induced phase transition in CsCuCl3. The present article describes the salient features of the various high temperature techniques developed and high temperature crystallographic studies made.