Anisotropic lattice thermal expansion of PbFeBO4: A study by X-ray and neutron diffraction, Raman spectroscopy and DFT calculations
Anisotropic lattice thermal expansion of PbFeBO4: A study by X-ray and neutron diffraction, Raman spectroscopy and DFT calculations
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PbFeBO4 的各向异性晶格热膨胀：X 射线和中子衍射、拉曼光谱和 DFT 计算的研究
DOI：
10.1016/j.materresbull.2014.07.005
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发表时间：
2014
影响因子：
5.4
通讯作者：
Th. M.
中科院分区：
文献类型：
--
作者：
Murshed;Mendive;Nénert;Kalita;P- E. Linpinska;A. L. Cornelius;A. L.;Huq;Gesing;Th. M.
研究了莫来石型PbFeBO4的晶格热膨胀。度量参数的热膨胀系数是从10 K和700 K之间的随温度变化的中子和X射线粉末衍射收集的复合数据获得的。采用扩展的Grüneisen一阶近似对零压状态方程进行了体积热膨胀建模。该模型的加性框架包括调和势、准调和势和内禀非调和势，用来描述内能随温度的变化。在DFT模拟过程中，在零压力和0 K的晶胞体积进行了优化。用DFT计算了0 K时布里渊区Γ点的光学拉曼模的谐波频率，为实验频率的归属和交叉校验提供了帮助。低温拉曼谱在反铁磁区表现出明显的反常，导致部分声子软化或硬化。选定的模式进行了分析，使用修改后的Klemens模型。频率的移动和线宽的加宽有助于理解PbO4，FeO 6和BO 3多面体的非谐振动行为作为温度的函数。
The lattice thermal expansion of mullite-type PbFeBO4is presented in this study. The thermal expansion coefficients of the metric parameters were obtained from composite data collected from temperature-dependent neutron and X-ray powder diffraction between 10 K and 700 K. The volume thermal expansion was modeled using extended Grüneisen first-order approximation to the zero-pressure equation of state. The additive frame of the model includes harmonic, quasi-harmonic and intrinsic anharmonic potentials to describe the change of the internal energy as a function of temperature. The unit-cell volume at zero-pressure and 0 K was optimized during the DFT simulations. Harmonic frequencies of the optical Raman modes at theΓ-point of the Brillouin zone at 0 K were also calculated by DFT, which help to assign and crosscheck the experimental frequencies. The low-temperature Raman spectra showed significant anomaly in the antiferromagnetic regions, leading to softening or hardening of some phonons. Selected modes were analyzed using a modified Klemens model. The shift of the frequencies and the broadening of the line-widths helped to understand the anharmonic vibrational behaviors of the PbO4, FeO6and BO3polyhedra as a function of temperature.