The thermal expansion of NH₄TcO₄ and NH₄ReO₄ between 97 and 500 K has been established using variable temperature synchrotron X-ray diffraction. Both oxides display a tetragonal scheelite-type structure over the temperature range. The observed anomalous thermal expansion is associated with disorder in the orientation of the NH₄ groups and the presence of anisotropic, equatorial and axial, interactions between the H atoms and the BO₄ tetrahedra. The importance of the hydrogen interactions was verified by a study of the isostructural compound NaReO₄ over a similar temperature range. The differences in the details of the Negative Thermal Expansion (NTE) behaviour of NH₄TcO₄ and NH₄ReO₄ is a consequence of differences in the H-BO₄ interactions due to changes in the B-O bond lengths within the BO₄ groups. Both ammonium salts decompose when heated above ∼500 K.

NH ₄ TcO ₄和NH ₄ ReO ₄在97 K至500 K之间的热膨胀已通过使用变温同步加速器X射线衍射确定。两种氧化物在该温度范围内均显示出四方白钨矿型结构。观察到的异常热膨胀与NH ₄基团的取向无序以及H原子与B O ₄四面体之间存在各向异性的，赤道的和轴向的相互作用有关。氢相互作用的重要性已通过对同构化合物NaReO ₄的研究得到证实。在相似的温度范围内。在NH的负热膨胀（NTE）行为的细节上的不同₄ TCO ₄和NH ₄ REO ₄是在H-差异的后果乙ö ₄相互作用由于变化乙所述内-O键长乙O ₄组。当加热到约500 K以上时，两种铵盐都会分解。