Abstract MnTe films exhibit a remarkable change in physical properties upon polymorphic transformation from β (wurtzite-type) to α (nickeline-type) phase. In this study, the mechanism of the β to α transformation in MnTe films capped with a tungsten layer during isothermal annealing at 500 °C was investigated. X-ray diffraction analyses revealed that the out-of-plane c-axis orientation was maintained during the polymorphic transformation. High-resolution transmission electron microscopy revealed that the β-phase transformed to the α-phase via a β′-phase which has a wurtzite-type structure as the β-phase but with a slight difference in the coordinates of the Te atoms. The β → β′ transformation was induced by the puckering process during which Mn- and Te-atomic planes shift in opposite directions along the c-axis, whereas the β′ → α transformation was induced by a buckling process during which pairs of Mn- and Te-atomic planes alternately move to the opposite directions along the 210 direction. Meanwhile, in the MnTe film without the tungsten capping layer, the out-of-plane c-axis orientation was not retained during the polymorphic transformation. These results imply that the sequential two-stage polymorphic transformation maintaining the out-of-plane c-axis orientation is caused by the constraint on the MnTe film induced by the tungsten capping layer.

中文翻译：

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多晶MnTe薄膜中通过β'相从β到α的连续两阶段位移转变

摘要 MnTe 薄膜在从β（纤锌矿型）到α（镍碱型）相的多晶型转变过程中表现出显着的物理性质变化。在这项研究中，研究了在 500 °C 等温退火期间用钨层覆盖的 MnTe 薄膜中 β 到 α 转变的机制。X 射线衍射分析表明，在多晶型转变过程中保持了面外 c 轴取向。高分辨率透射电子显微镜显示，β相通过具有纤锌矿型结构的β'相转变为α相，β相具有纤锌矿型结构，但Te原子的坐标略有不同。β → β' 转变是由褶皱过程引起的，在此过程中，Mn 和 Te 原子平面沿 c 轴向相反方向移动，而β'→α转变是由屈曲过程引起的，在此过程中，成对的Mn-和Te-原子平面沿210方向交替移动到相反的方向。同时，在没有钨覆盖层的 MnTe 膜中，面外 c 轴取向在多晶型转变过程中没有保留。这些结果意味着保持面外 c 轴取向的连续两阶段多晶型转变是由钨覆盖层引起的对 MnTe 膜的约束引起的。