Temperature Validation for In-Situ X-ray Diffraction Below Ambient Temperatures
Validation of the temperature readout is an essential requirement for high quality non-ambient X-ray diffraction (XRD) experiments. This is typically done by comparing phase transition temperatures of well-known reference materials to the literature values. While many different reference materials for validation at temperatures above room temperature are known, finding suitable materials for validation below ambient temperatures is challenging.
The relevance of in-situ XRD at varying temperatures is steadily increasing in academia and industry. Today, a large variety of different non-ambient attachments covering a wide range of temperatures is commercially available. This catalogue is extended even further by customized and self-made solutions that are specially designed for certain facilities or experiments.
One major challenge in the design of any non-ambient XRD attachment is the temperature measurement. The temperature reported by the thermosensor inside the attachment always deviates slightly from the actual temperature of the sample surface where the X‑rays are diffracted from. The magnitude of the deviation depends on the heater design, the sample properties, the contact surface between sample and heater, and even the gas atmosphere surrounding the sample. In addition, depending on the thermal properties, size and shape of the sample, and on the type of heater employed, there might be a significant temperature gradient within the sample. While certain heater designs, such as environmental (oven) heaters, can improve temperature accuracy and homogeneity in comparison to other designs, such as direct heaters, a slight deviation in temperature is inevitable.
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