Bevara Samatha, Achary S Nagabhusan, Garg Nandini, Chitnis Abhishek, Sastry P U, Shinde A B, Krishna P Siva Ram, Tyagi Avesh Kumar
Chemistry Division, Bhabha Atomic Research Centre , Trombay, Mumbai 400085, India.
Homi Bhabha National Institute , Anushakti Nagar, Mumbai 400094, India.
Inorg Chem. 2018 Feb 19;57(4):2157-2168. doi: 10.1021/acs.inorgchem.7b03028. Epub 2018 Feb 3.
The structural stability and phase transition behavior of tetragonal (I4/m) hollandite type KFeTiO have been investigated by in situ high pressure X-ray diffraction using synchrotron radiation and a diamond anvil cell as well as by variable temperature powder neutron and X-ray diffraction. The tetragonal phase is found to be stable in a wider range of temperatures, while it reversibly transforms to a monoclinic (I2/m) structure at a moderate pressure, viz. 3.6 GPa. The pressure induced phase transition occurs with only a marginal change in structural arrangements. The unit cell parameters of ambient (t) and high pressure (m) phases can be related as a ∼ a, b ∼ c, and c ∼ b. The pressure evolution of the unit cell parameters indicates anisotropic compression with β = β ≥ β in the tetragonal phase and becomes more anisotropic with β ≪ β < β in the monoclinic phase. The pressure-volume equations of state of both phases have been obtained by second order Birch-Murnaghan equations of state, and the bulk moduli are 122 and 127 GPa for tetragonal and monoclinic phases, respectively. The temperature dependent unit cell parameters show nearly isotropic expansion, with marginally higher expansion along the c-axis compared to the a- and b-axes. The tetragonal to monoclinic phase transition occurs with a reduction of unit cell volume of about 1.1% while the reduction of unit cell volume up to 6 K is only about 0.6%. The fitting of temperature dependent unit cell volume by using the Einstein model of phonons indicates the Einstein temperature is about 266(18) K.
利用同步辐射和金刚石对顶砧池通过原位高压X射线衍射以及变温粉末中子和X射线衍射研究了四方（I4/m）钡铁钛矿型KFeTiO的结构稳定性和相变行为。发现四方相在更宽的温度范围内是稳定的，而在中等压力（即3.6 GPa）下它可逆地转变为单斜（I2/m）结构。压力诱导的相变发生时结构排列仅有微小变化。常压（t）相和高压（m）相的晶胞参数可表示为a ∼ a、b ∼ c和c ∼ b。晶胞参数的压力演化表明，四方相中β = β ≥ β时存在各向异性压缩，而单斜相中β ≪ β < β时各向异性更强。通过二阶Birch-Murnaghan状态方程获得了两相的压力-体积状态方程，四方相和单斜相的体模量分别为122 GPa和127 GPa。与温度相关的晶胞参数显示出近乎各向同性的膨胀，沿c轴的膨胀略高于a轴和b轴。四方相向单斜相的转变伴随着晶胞体积约1.1%的减小，而在高达6 K时晶胞体积的减小仅约0.6%。利用声子的爱因斯坦模型对与温度相关的晶胞体积进行拟合表明，爱因斯坦温度约为266(18) K。
