In-situ, in air, high-temperature phase transformations in rare-earth niobates and titanium oxides (dysprosium and yttrium) using a thermal-image furnace.

摘要

Thermal-image furnaces afford two major advantages over the conventional resistance heating systems for high-temperature studies of oxides in air, namely: (i) the highly localized heating allows temperatures in excess of 2500°C to be reached in air or in an oxidizing atmosphere, and (ii) no sample contamination from volatile furnace components since the sample is heated by absorption of a focused, high intensity light beam.; In this work, we developed a compact furnace powered by four halogen infrared reflector lamps (150 W each), for in-situ high-temperature studies using synchrotron radiation. The primary objective was to evaluate the feasibility of the thermal-image technique for in-situ, in air, studies of high-temperature phase transformations in oxide ceramics. Specifically, the issues of temperature measurement and reliability of results obtained in comparison with published literature were addressed.; The use of a co-existent “in-situ thermometer” was found to be a viable method to monitor the sample temperature in the image “hot-spot”. Studies of YNbO₄ and DyNbO₄ revealed the existence of a new cubic phase at elevated temperatures beyond the commonly known ferroelastic monoclinic-to-paraelastic tetragonal transformations. A series of high-temperature powder patterns of the pure hexagonal phase of DY₂TiO₅ was also collected in-situ, in air.