Near-Zero Thermal Expansion and Phase Transitions in HfMg(1−x)Zn(x)Mo(3)O(12)

The effects of Zn(2+) incorporation on the phase formation, thermal expansion, phase transition, and vibrational properties of HfMg(1−x)Zn(x)Mo(3)O(12) are investigated by XRD, dilatometry, and Raman spectroscopy. The results show that (i) single phase formation is only possible for x ≤ 0.5, otherwise, additional phases of HfMo(2)O(8) and ZnMoO(4) appear; (ii) The phase transition temperature from monoclinic to orthorhombic structure of the single phase HfMg(1−x)Zn(x)Mo(3)O(12) can be well-tailored, which increases with the content of Zn(2+); (iii) The incorporation of Zn(2+) leads to an pronounced reduction in the positive expansion of the b-axis and an enhanced negative thermal expansion (NTE) in the c-axes, leading to a near-zero thermal expansion (ZTE) property with lower anisotropy over a wide temperature range; (iv) Replacement of Mg(2+) by Zn(2+) weakens the Mo–O bonds as revealed by obvious red shifts of all the Mo–O stretching modes with increasing the content of Zn(2+) and improves the sintering performance of the samples which is observed by SEM. The mechanisms of the negative and near-ZTE are discussed.