ReO₃-type ABF₆, are of interest as low and negative thermal expansion (NTE) materials. As only cubic ABF₆ display NTE, the occurrence of phase transitions needs to be understood. The thermal expansion, phase behavior on heating and compression, and compressibilities of MnNbF₆ and ZnNbF₆ were examined by synchrotron powder diffraction. MnNbF₆ undergoes a first order rhombohedral to cubic transition at ~315 K, but ZnNbF₆ is rhombohedral over the temperature range examined (~100 to 500 K). MnNbF₆ displays zero thermal expansion at ~380 K and NTE above this temperature. MnNbF₆ became completely rhombohedral on initial compression and transformed to an unidentified phase at ~ 6 GPa. Rhombohedral MnNbF₆ is initially elastically very soft (K₀ ~ 5 GPa), but stiffens considerably on compression. Below ~3.5 GPa it displays negative linear compressibility. ZnNbF₆ remained rhombohedral over the entire pressure range examined (0 - ~4 GPa) and displayed a similar stiffening on compression.

ReO ₃型ABF ₆作为低热膨胀率和负热膨胀（NTE）材料而受到关注。由于只有立方ABF ₆显示NTE，因此需要了解相变的发生。通过同步加速器粉末衍射检查了MnNbF ₆和ZnNbF ₆的热膨胀，加热和压缩时的相行为以及可压缩性。MnNbF ₆在〜315  K处经历一阶菱形到立方相变，但是ZnNbF ₆在所检查的温度范围（〜100至500  K）上呈菱形。MnNbF ₆在〜380  K时显示零热膨胀，在此温度以上显示NTE。MnNbF ₆在初始压缩时变成完全菱面体，并在 〜6 GPa处转变为不确定的相。菱形MnNbF ₆是最初弹性非常柔软（K ₀〜5  GPa）的，但是变硬相当上压缩。低于 〜3.5 GPa时，它显示出负的线性可压缩性。ZnNbF ₆在检查的整个压力范围（0- 〜4  GPa）内保持菱形，并且在压缩时表现出类似的变硬。