Temperature- and pressure-dependent lattice behaviour of RbFe(MoO4)2
Temperature- and pressure-dependent lattice behaviour of RbFe(MoO4)2
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RbFe(MoO4)2 与温度和压力相关的晶格行为
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发表时间：
2010
期刊：
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通讯作者：
K. Hermanowicz
中科院分区：
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作者：
A. Waśkowska;L. Gerward;J. Staun Olsen;W. Morgenroth;M. Ma̧czka;K. Hermanowicz
三角形RbFe(MoO4)2在TN = 3.8 K以下为三角形晶格上的准二维反铁磁体，晶体在Tc = 190 K处也表现出与从到的对称性变化有关的结构相变。我们提出了这种材料的温度和压力依赖特性的背景下，对对称性和晶体性质的模糊意见低于Tc。单晶x射线衍射表明，在100-300 K范围内，单晶胞的温度依赖演化具有很强的各向异性，在Tc处具有明显的不连续变化。这种转变与由于体积减小而产生的自发应变有关。该结构通过在（a,b）基面上旋转共享角的刚性MoO4和FeO6多面体来释放应变。红外振动波数的温度依赖性在Tc附近表现出微弱的变化，这与从到的对称变换是一致的。高压x射线粉末衍射表明材料非常柔软，但在高压下有一定的硬化。零压体积模量B0 = 7.9(6) GPa，压力导数B0′= 10(1)。压缩曲线可以用一个单一的状态方程来描述，对应于三角形电池，最高可达5 GPa。在5 GPa以上出现非晶化现象，并随着压力的增加逐渐增大，表明高压结构存在热力学不稳定性。
Trigonal RbFe(MoO4)2 is a quasi-two-dimensional antiferromagnet on a triangular lattice below TN = 3.8 K, The crystal exhibits also a structural phase transition at Tc = 190 K related to symmetry change from to . We present the temperature- and pressure-dependent characteristics of this material in the context of ambiguous opinions on the symmetry and crystal properties below Tc. A single-crystal x-ray diffraction shows that the temperature-dependent evolution of the unit cell in the range 100–300 K is strongly anisotropic with markedly discontinuous changes at Tc. The transition is connected with a spontaneous strain developing in effect of the volume decrease. The structure releases the strain by rotation of corner-sharing rigid MoO4 and FeO6 polyhedra in the (a,b) basal plane. The temperature dependence of the IR vibrational wavenumbers exhibits weak changes near Tc, which are consistent with the symmetry transformation from to . High-pressure x-ray powder diffraction indicates that the material is extremely soft but with some stiffening at high pressure. The zero-pressure bulk modulus is B0 = 7.9(6) GPa and the pressure derivative is B0′ = 10(1). The compression curve can be described by a single equation of state, corresponding to the trigonal cell, up to 5 GPa. An amorphization appearing above 5 GPa and increasing gradually on further pressure increase suggests the thermodynamic instability of the high-pressure structure.