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In-situ high temperature studies of a negative thermal expansion coefficient material, ZrW2O8


Time resolved, in situ heating XRD experiments provide data under chosen non-ambient conditions that are vital for the research and development of many materials. Such a capability circumvents changes in material properties that are normal upon transferring the material from an oven to the diffractometer.


One piece of valuable information from a variable temperature experiment pertains to phase and structural changes. The ceramic ZrW2O8 is a well-known material with negative thermal expansion over a wide temperature range, 0-1050 K. In situ heating of ZrW2O8 was performed using the High Temperature Attachment (HTA) unit on the Ultima IV. Heating can be performed up to 1500°C on this unit in vacuum or under any inert atmosphere, with different types of heating and cooling cycles. Data were collected using the high-speed, D/teX detector with a total of four minutes for each powder pattern. A 3D overlay of the in situ XRD patterns of ZrW2O8 in Figure 1 indicates a phase change at 150°C, and a shift in peak positions towards lower 2θ as a function of temperature. A Rietveld refinement (using structureless fitting module) of ZrW2O8 powder patterns collected from RT to 700°C relate these changes to a decrease in lattice constant and an order disorder transition in ZrW2O8 with a change in space group from P213 to Pa3 upon heating as shown in Table 1.

High Temp XRD StudyHigh Temp Study table