A 2 3+ B 2 4+ O 7（A = Lu 3+ –La 3+，B = Zr 4+，Hf 4+的Weberite型，烧绿石和缺陷萤石结构的稳定性的第一性原理研究，Sn 4+和Ti 4+）,The Journal of Physical Chemistry C

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A ₂³⁺B ₂⁴⁺ O ₇（A = Lu ³⁺ –La ³⁺，B = Zr ⁴⁺，Hf ⁴⁺的Weberite型，烧绿石和缺陷萤石结构的稳定性的第一性原理研究，Sn ⁴⁺和Ti ⁴⁺）
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2020-08-24 , DOI: 10.1021/acs.jpcc.0c05443
Ushio Matsumoto _{1,

2} , Takafumi Ogawa ₁ , Satoshi Kitaoka ₃ , Hiroki Moriwake ₁ , Isao Tanaka _{1,

2}

Affiliation

首先，系统地研究了一系列A ₂B ₂ O ₇（A = Lu ³⁺ –La ^{3 +}，B = Zr ⁴⁺，Hf ⁴⁺，Sn ⁴⁺和Ti ⁴⁺）化合物的晶体结构和能量学。-原理计算。在实验上，已知它们会形成烧绿石或萤石缺陷结构。最近，在Ho ₂ Zr ₂ O _7中报道了韦伯石型有序的形成。在这项研究中，我们对组成Yb ₂ Ti ₂进行了详尽的结构搜索O ₇，发现最低能量的结构是三斜辉石型结构，其特征在于Yb和Ti层交替。从第一性原理声子计算得出的自由能表明，Yb ₂ Ti ₂ O ₇的韦伯石型和烧绿石结构之间的转变温度为550K 。还比较了韦伯石型和烧绿石结构的能量。A ₂B ₂ O ₇组成。作为一般趋势，发现随着A ^3+的增加，韦伯石型结构的稳定性相对于烧绿石结构增加。阳离子半径减小。还报道了使用特殊的准随机结构估算的无序缺陷萤石结构的能量。发现当A ³⁺阳离子半径小时，在A ₂ Zr ₂ O ₇和A ₂ Hf ₂ O ₇中的高温下，这种缺陷萤石结构的形成在能量上更有利。目前的结果与先前报道的实验结果一致。

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First-Principles Study on the Stability of Weberite-Type, Pyrochlore, and Defect-Fluorite Structures of A23+B24+O7 (A = Lu3+–La3+, B = Zr4+, Hf4+, Sn4+, and Ti4+)

Crystal structures and energetics of a series of A₂B₂O₇ (A = Lu³⁺–La³⁺, B = Zr⁴⁺, Hf⁴⁺, Sn⁴⁺, and Ti⁴⁺) compounds were systematically investigated using first-principles calculations. Experimentally, they are known to form either pyrochlore or defect-fluorite structures. Recently, formation of a weberite-type ordering was reported in Ho₂Zr₂O₇. In this study, we performed an exhaustive structure search for composition Yb₂Ti₂O₇ and found that the lowest-energy structure is a triclinic weberite-type structure characterized by alternating Yb and Ti layers. Free energies from first-principles phonon calculations suggest that the transition temperature between the weberite-type and pyrochlore structures of Yb₂Ti₂O₇ is 550 K. The energies of the weberite-type and pyrochlore structures are also compared for a wide range of A₂B₂O₇ compositions. As a general trend, it is found that the stability of the weberite-type structure increases relative to the pyrochlore structure as the A³⁺ cation radius decreases. Energies of disordered defect-fluorite structures estimated using special quasi-random structures are also reported. The formation of such defect-fluorite structures is found to be more energetically favorable at high temperatures in A₂Zr₂O₇ and A₂Hf₂O₇ when the A³⁺ cation radius was small. The present results are consistent with previously reported experimental results.

更新日期：2020-09-18

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