The orthorhombic-to-monoclinic phase transition in NbCrP – Peierls distortion of the chromium chain

IF 0.9 4区材料科学 Q3 CRYSTALLOGRAPHY

Zeitschrift Fur Kristallographie-Crystalline Materials Pub Date : 2021-12-02 DOI:10.1515/zkri-2021-2058

C. Paulsen, Jutta Kösters, S. Seidel, Yoshiki Kuwata, H. Kotegawa, H. Tou, H. Sugawara, H. Harima, R. Pöttgen

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引用次数: 2

Abstract

Abstract The equiatomic metal-rich phosphide NbCrP shows a structural phase transition around 125 K. The structures of the high- and low-temperature modifications were refined from single crystal X-ray diffractometer data of an un-twinned crystal: TiNiSi type, Pnma, a = 619.80(2), b = 353.74(4), c = 735.24(6) pm, wR = 0.0706, 288 F 2 values, 20 variables at 240 K and P121/c1, a = 630.59(3), b = 739.64(4), c = 933.09(5) pm, β = 132.491(6)°, wR = 0.0531, 1007 F 2 values, 57 variables at 90 K. The structural phase transition is of a classical Peierls type. The equidistant chromium chain in HT-NbCrP (353.7 pm Cr–Cr) splits pairwise into shorter (315.2 pm) and longer (373.2 pm) Cr–Cr distances. This goes along with a strengthening of Cr–P bonding. The superstructure formation is discussed on the basis of a group–subgroup scheme. Electronic structure calculations show a lifting of band degeneracy. Protection of the non-symmorphic symmetry of space group Pnma is crucial for the phase transition. The estimated charge modulation is consistent with the interpretation as Peierls transition.

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铬链NbCrP - Peierls畸变的正交向单斜相变

富金属等原子磷化物NbCrP在125 K左右发生结构相变。利用单晶x射线衍射仪数据对高低温改性的结构进行了细化:TiNiSi型，Pnma, a = 619.80(2)， b = 353.74(4)， c = 735.24(6) pm, wR = 0.0706, 288 f2值，240 K时20个变量;P121/c1, a = 630.59(3)， b = 739.64(4)， c = 933.09(5) pm， β = 132.491(6)°，wR = 0.0531, 1007 f2值，90 K时57个变量。结构相变是典型的佩尔型相变。HT-NbCrP中的等距铬链(353.7 pm Cr-Cr)成对分裂成较短(315.2 pm)和较长(373.2 pm)的Cr-Cr链。这伴随着Cr-P键合的加强。在群-子群方案的基础上讨论了上层建筑的形成。电子结构计算表明带简并度有所提高。保护空间群Pnma的非对称对称性是相变的关键。估计的电荷调制与佩尔跃迁的解释一致。

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来源期刊

Zeitschrift Fur Kristallographie-Crystalline Materials CRYSTALLOGRAPHY-

CiteScore

2.00

自引率

16.70%

发文量

期刊介绍： Zeitschrift für Kristallographie – Crystalline Materials was founded in 1877 by Paul von Groth and is today one of the world’s oldest scientific journals. It offers a place for researchers to present results of their theoretical experimental crystallographic studies. The journal presents significant results on structures and on properties of organic/inorganic substances with crystalline character, periodically ordered, modulated or quasicrystalline on static and dynamic phenomena applying the various methods of diffraction, spectroscopy and microscopy.