InOOH压致氢键对称化及其弹性性质

利用第一性原理研究了InOOH在高压下的氢键对称化行为及其对InOOH弹性等性质的影响.结果表明约在18 GPa时InOOH中的氢键发生了对称化转变,导致轴比率b/c对压力的斜率由负值变为正值;压缩弹性常数、非对角弹性常数、体积模量和纵波波速出现异常增加,如体积模量增加了20%—40%.高压下InOOH弹性性质呈现出更加明显的各向异性.常压下InOOH呈现韧性,且伴随着氢键对称化韧性异常增加.对畸变金红石型MOOH(M=Al,In,Ga,Fe,Cr)化合物在高压下的弹性性质转变与氢键性质转变的耦合规律进行了初探.

Pressure-induced hydrogen bond symmetrization of InOOH and its elastic properties

Pressure-induced hydrogen bond symmetrization of InOOH as well as its effects on the elastic properties is investigated by first-principles simulation. The results indicate that the hydrogen bond in InOOH symmetrized at about 18 GPa, resulting in the pressure derivative of the b/c axial ratio changing from negative to positive. While the a/c axial ratio increases with the increasing pressure over a range of 0-40 GPa, its pressure derivative does not change significantly across the hydrogen bond symmetrization. In the text, ‘A-InOOH’ denotes the asymmetric hydrogen bond phase and ‘S-InOOH’ refers to the symmetric hydrogen bond phase. The compressional and off-diagonal elastic constants, bulk modulus B, Poisson's ratio ν, B/G (G represents shear modulus) and longitudinal wave velocity V_P increase with the increasing pressure in both A-InOOH and S-InOOH. These properties of A-InOOH are significantly smaller than those of S-InOOH, and therefore they increase abnormally during the hydrogen bond symmetrization, such as a 20%-40% increase of the bulk modulus. Shear modulus G and Young's modulus E increase with the increasing pressure in A-InOOH, but decrease with the increasing pressure in S-InOOH, implying that hydrogen bond symmetrization would change their pressure evolution trends obviously. Shear elastic constant C₄₄ and shear wave velocity V_S decrease with the increasing pressure in both A-InOOH and S-InOOH, and more quickly in the latter, indicating that the structure change of hydrogen bond would change their pressure evolution rates. The Young's moduli along the100],010] and001] directions increase with the increasing pressure in A-InOOH, while decrease with the increasing pressure in S-InOOH, and those along the110],110],110] and110] directions always increase with the increasing pressure over a range of 0-40 GPa. The anisotropy and toughness of InOOH increase with the increasing pressure in both A-InOOH and S-InOOH, and the hydrogen bond symmetrization results in abnormal increase. In the materials containing hydrogen bonds, the effects of hydrogen bond symmetrization on different compressional elastic constants depend on the hydrogen bond projection on corresponding axes:the bigger the projection, the more significant the effect is. InOOH has an obviously smaller bulk modulus than δ-AlOOH. The dominant reason is that the In³⁺ radius (0.81 Å, 1 Å=0.1 nm) is larger than Al³⁺ radius (0.50 Å), resulting in the weaker interaction between In³⁺ and O^2- than that between Al³⁺ and O^2-. In addition, InOOH has more vacancies than δ-AlOOH. Combining with previous investigations on other rutile-distorted MOOH (M= Al, Ga, Fe, Cr), we can infer that the axial ratios, elastic properties and wave velocities of all MOOH materials have similar pressure evolutions to those of InOOH, and the hydrogen bond symmetrization has similar effects on the properties of MOOH.