High-pressure, low-temperature optical and X-ray diffraction studies of semiconducting and incommensurate materials

In order to investigate the effects of both high-pressure and low-temperature on materials, a new diamond anvil cell and gasket system has been developed which has increased stability over the previous design. In addition, a system has been designed to perform optical absorption measurements at high-pressure and low-temperature in a diamond anvil cell. Successful high-pressure, low-temperature Raman measurements have been performed on both Cs₂MOS ₄ and KTbP₂Se₆ using the newly designed cell. Two pressure induced phase transitions have been observed at 77 K in Cs ₂MOS₄ and a single pressure induced phase transition has been observed at 77 K in KTbP₂Se₆. High pressure, energy dispersive X-ray diffraction measurements of (NH₄)₂ ZnCl₄ have also been performed at constant temperatures up to 150°C. Values of the calculated adiabatic bulk modulus and experimentally determined isothermal bulk modulus for (NH₄)₂ ZnCl₄ and other materials in the A₂BX₄ have been compiled and discussed.