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首页> 外文期刊>Physical review >Neutron diffraction measurements and first-principles study of thermal motion of atoms in select M_(n+1)AX_n and binary MX transition-metal carbide phases
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Neutron diffraction measurements and first-principles study of thermal motion of atoms in select M_(n+1)AX_n and binary MX transition-metal carbide phases

机译：M_（n + 1）AX_n和二元MX过渡金属碳化物相中原子的热中子衍射测量和第一性原理研究

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摘要

Herein, we compare the thermal vibrations of atoms in select ternary carbides with the formula M_(n+1) AX_n ("MAX phases," M = Ti, Cr; A = Al, Si, Ge; X = C, N) as determined from first-principles phonon calculations to those obtained from high-temperature neutron powder diffraction studies. The transition metal carbides TiC, TaC, and WC are also studied to test our methodology on simpler carbides. Good qualitative and quantitative agreement is found between predicted and experimental values for the binary carbides. For all the MAX phases studied-Ti_3SiC_2, Ti_3GeC_2, Ti_2AlN, Cr_2GeC and Ti_4AlN_3-density functional theory calculations predict that the A element vibrates with the highest amplitude and does so anisotropically with a higher amplitude within the basal plane, which is in line with earlier results from high-temperature neutron diffraction studies. In some cases, there are quantitative differences in the absolute values between the theoretical and experimental atomic displacement parameters (ADPs), such as reversal of anisotropy or a systematic offset of temperature-dependent ADPs. The mode-dependent Grueneisen parameters are also computed to explore the anharmonicity in the system.
机译：在这里，我们将选择的三元碳化物中的原子的热振动与公式M_（n + 1）AX_n（“ MAX phases”，M = Ti，Cr; A = Al，Si，Ge; X = C，N）进行比较。从第一性原理声子计算得出的结果到从高温中子粉末衍射研究获得的结果。还研究了过渡金属碳化物TiC，TaC和WC，以测试我们在较简单的碳化物上的方法。在二元碳化物的预测值和实验值之间找到了良好的定性和定量一致性。对于研究的所有MAX相-Ti_3SiC_2，Ti_3GeC_2，Ti_2AlN，Cr_2GeC和Ti_4AlN_3-密度泛函理论计算预测，A元素以最高振幅振动，并且各向异性地以较高的振幅在基平面内振动，这与早期高温中子衍射研究的结果。在某些情况下，理论和实验原子位移参数（ADP）之间的绝对值之间存在定量差异，例如各向异性的逆转或与温度有关的ADP的系统性偏移。还计算了与模式有关的Grueneisen参数，以探索系统中的非谐性。

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