Phonon Dynamics in Anisotropic Dilute CuAl 1–x Fe x O 2 Delafossite Alloys by a Weighted Dynamical Matrix Approach
Phonon Dynamics in Anisotropic Dilute CuAl 1–x Fe x O 2 Delafossite Alloys by a Weighted Dynamical Matrix Approach
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采用加权动力学矩阵方法研究各向异性稀 CuAl 1–x Fe x O 2 德拉铁矿合金中的声子动力学
DOI：
10.1021/acs.jpcc.9b09402
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Johnson, M. B.
中科院分区：
文献类型：
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作者：
Aziziha, M.;Akbarshahi, S.;Ghosh, S.;Pramanik, P.;Lewis, J. P.;Romero, A. H.;Thota, S.;Seehra, M. S.;Johnson, M. B.
在这里，我们报告了一个新的多功能的声子模式的计算方法，适用于各向异性，稀合金与津贴的各种合金元素。这种方法具有显着的优势，比以前报道的方法，特别是对于这种复杂合金的晶格动力学。我们使用这种方法来模拟铁掺杂的CuAl 1-xFexO 2（x= 0，0.01，0.05，和0.10）铜铁矿粉的稀合金的振动模式的影响。这些样品的结构特征与X射线衍射（XRD）结合Rietveld精修测量其晶格参数和拉曼和FTIR光谱测量光学声子频率。为了将XRD的实验结果与晶格参数的计算结果进行比较，我们使用了0-0.1范围内的无序超晶胞。这两个结果都符合Vegard定律。对于声子计算，使用无序超晶胞的方法是不可行的，因为它在计算上太昂贵。相反，我们开发了我们的加权动力学矩阵（WDM）的方法，使用一个简单有序的超晶胞的力常数计算的CuAlO 2和CuFeO 2母端点，并结合它们使用WDM的方法导致一个有效的介质随机合金的振动模式计算。计算上，当Fe取代Al（increasingx），键长的增加被观察到导致所有的声子模式vsx的峰位置的红移，与实验观察到的趋势一致。
Here we report a new versatile approach for the calculation of phonon modes which is applicable to anisotropic, dilute alloys with allowance for a large variety of alloying elements. This approach has significant advantages over previously reported methods, especially for the lattice dynamics of such complex alloys. We use this approach to model the effects of Fe-doping on the vibrational modes in dilute alloys of CuAl1–xFexO2(x= 0, 0.01, 0.05, and 0.10) delafossite powders. These samples were structurally characterized with X-ray diffraction (XRD) combined with Rietveld refinement to measure their lattice parameters and Raman and FTIR spectroscopies to measure optical phonon frequencies. To compare experimental results from XRD with calculations for lattice parameters, we use a disordered supercell forxin the range 0–0.1. Both results agree well with Vegard’s law. For the phonon calculations, an approach using a disordered supercell is not feasible because it is too computationally expensive. Instead, we developed our weighted dynamical matrix (WDM) approach that uses a straightforward ordered supercell for force-constant calculations of the CuAlO2and CuFeO2parent end points, and combines them using a WDM approach leading to an effective medium for vibrational mode calculation in random alloys. Computationally, when Fe is substituted for Al (increasingx), an increase in the bond length is observed leading to a red-shift in the peak positions in all of the phonon modes vsx, in agreement with the experimentally observed trend.