Insights into Phase Control and Stabilisation of Metastable β-phase AMoO4 (A = Ni, Co, Ni/Co) Solid Solutions

Nickel- and cobalt-based molybdates, AMoO4, where A = Ni, Co, or Ni/Co, are of significant interest owing to their temperature-dependent phase behaviour and promising performance in electrochemical applications, particularly glucose sensing. This work explores the thermal stability and phase transitions of a series of Co and Ni molybdate solid solutions using in-situ variable-temperature X-ray diffraction (VT-XRD), with a focus on stabilising the high-temperature β-NiMoO4 phase at ambient conditions through cobalt substitution. VT-XRD measurements reveal that pristine NiMoO4 undergoes an α to β phase transition at approximately 300 °C. Progressive addition of Co systematically lowers the transition temperature to 200 °C for 5% Co and as low as 100 °C for 50% Co-substituted samples. Notably, pure CoMoO4 exhibits no β to α reverse transformation upon cooling, indicating kinetic stabilisation of the β-phase. These results demonstrate a strong compositional control over the α↔β phase transition in AMoO4 materials and highlight cobalt substitution as an effective strategy for stabilising the high-temperature β-NiMoO4 phase at or near room temperature.以镍、钴为阳离子的钼酸盐AMoO₄（其中A为Ni、Co或Ni/Co混合体系）因其温度依赖的相转变行为，以及在电化学应用（尤其是葡萄糖传感）中展现出的优异性能而受到广泛关注。本研究采用原位变温X射线衍射（in-situ variable-temperature X-ray diffraction, VT-XRD）技术，对一系列钴基与镍基钼酸盐固溶体的热稳定性及相转变行为进行探究，重点关注通过钴掺杂在室温条件下稳定高温相β-NiMoO₄的策略。VT-XRD测试结果显示，纯相NiMoO₄在约300℃时发生α相向β相的转变；随着钴掺杂比例逐步提升，相转变温度系统性降低：5%钴掺杂样品的转变温度降至200℃，而50%钴掺杂样品的转变温度可低至100℃。值得注意的是，纯相CoMoO₄在冷却过程中未出现β相向α相的逆转变，表明β相通过动力学机制得到了稳定。上述结果证实，通过组分调控可有效实现AMoO₄材料中α↔β相转变的精准控制，并证明钴掺杂是在室温或近室温条件下稳定高温相β-NiMoO₄的有效手段。