TY - JOUR
T1 - Sequential two-stage displacive transformation from β to α via β′ phase in polymorphic MnTe film
AU - Mori, Shunsuke
AU - Ando, Daisuke
AU - Sutou, Yuji
N1 - Funding Information:
This work was supported by the JSPS KAKENHI (Grant Number 18H02053 and 19J21117 ), the Mitsubishi Foundation and the Tohoku University Division for Interdisciplinary Advanced Research and Education (DIARE). We would like to thank Takamichi Miyazaki, Kosei Kobayashi, and Masatoshi Tanno for their assistance in TEM observations in this work.
Publisher Copyright:
© 2020 The Authors
PY - 2020/11
Y1 - 2020/11
N2 - 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.
AB - 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.
KW - Compound semiconductors
KW - Displacive transformation
KW - Phase transformation
KW - Sputtering
KW - Thin film
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U2 - 10.1016/j.matdes.2020.109141
DO - 10.1016/j.matdes.2020.109141
M3 - Article
AN - SCOPUS:85091230852
VL - 196
JO - International Journal of Materials in Engineering Applications
JF - International Journal of Materials in Engineering Applications
SN - 0264-1275
M1 - 109141
ER -