Thermal expansion coefficients of NH4ReO4 and NH4IO4 down to 58 K

Abstract
The linear coefficients of thermal expansion have been determined for NH4ReO4 and NH4IO4 down to 58 K. Below 100 K the values are normal with αa=1×10−5/K and αc=6×10−5/K. Between 100 and 300 K the coefficients are anamalous with αa=−10×10−5/K and αc=+20×10−5/K. The use of these materials as secondary temperature standards in x-ray and neutron diffraction is discussed.