Alves Dos Santos Edileide, França Jessica Kamily Pereira, Dos Santos Adenilson Oliveira, Nurrieli Andira, Do Carmo Danusa, Dos Reis Ricardo Donizeth, Moreira da Silva Luzeli
Centro de Ciências de Imperatriz (CCIM), Universidade Federal do Maranhão-UFMA, Maranhão, Brazil.
Brazilian Synchrotron Light Laboratory (LNLS), Brazilian Center for Research in Energy and Materials (CNPEM), Campinas, SP 13053-970, Brazil.
J Phys Condens Matter. 2023 Dec 28;36(13). doi: 10.1088/1361-648X/ad13d6.
Here we investigate the structural properties of the MnCoNiGe half-Heusler alloys under pressure up to 12 GPa by Synchrotron angle-dispersive x-ray diffraction (XRD). At room temperature and pressure, the compound exhibits only the hexagonal NiIn-type structure. Lowering the temperature to 100 K at ambient pressure induces an almost complete martensitic phase transformation to the orthorhombic TiNiSi-type structure. With increasing pressure, the stable orthorhombic phase gradually undergoes a reverse martensitic transformation. The hexagonal phase reaches 85% of the sample when applying 12 GPa of pressure at= 100 K. We further evaluated the bulk modulus of both hexagonal and orthorhombic phases and found similar values (123.1 ± 5.9 GPa for hexagonal and 102.8 ± 4.2 GPa for orthorhombic). Also, we show that the lattice contraction induced is anisotropic. Moreover, the high-pressure hexagonal phase shows a volumetric thermal contraction coefficient∼ -8.9(1) × 10Kwhen temperature increases from 100 to 160 K, evidencing a significant negative thermal expansion (NTE) effect. Overall, our results demonstrate that the reverse martensitic transition presented on MnCoNiGe induced either by pressure or temperature is related to the anisotropic contraction of the crystalline arrangement, which should also play a crucial role in driving the magnetic phase transitions in this system.
在这里，我们通过同步辐射角散射X射线衍射（XRD）研究了压力高达12 GPa时MnCoNiGe半赫斯勒合金的结构特性。在室温和常压下，该化合物仅呈现六方NiIn型结构。在常压下将温度降至100 K会引发几乎完全的马氏体相变，转变为正交TiNiSi型结构。随着压力增加，稳定的正交相逐渐经历逆马氏体相变。在100 K施加12 GPa压力时，六方相占样品的85%。我们进一步评估了六方相和正交相的体积模量，发现数值相近（六方相为123.1±5.9 GPa，正交相为102.8±4.2 GPa）。此外，我们表明诱导的晶格收缩是各向异性的。而且，高压六方相在温度从100 K升高到160 K时显示出约-8.9(1)×10⁻⁵ K⁻¹ 的体积热收缩系数，证明了显著的负热膨胀（NTE）效应。总体而言，我们的结果表明，由压力或温度诱导的MnCoNiGe上的逆马氏体转变与晶体排列的各向异性收缩有关，这在驱动该系统中的磁相变方面也应起关键作用。
