Negative thermal expansion in NbF_3 and NbOF_2:A comparative theoretical study |
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| Institution: | 1.International Laboratory for Quantum Functional Materials of Henan, and School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450052, China;2.Key Laboratory of Special Functional Materials of Ministry of Education, and School of Materials Science and Engineering, Henan University, Henan 475001, China |
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| Abstract: | Thermal expansion control is always an obstructive factor and challenging in high precision engineering field. Here,the negative thermal expansion of Nb F_3 and Nb OF_2 was predicted by first-principles calculation with density functional theory and the quasi-harmonic approximation(QHA). We studied the total charge density, thermal vibration, and lattice dynamic to investigate the thermal expansion mechanism. We found that the presence of O induced the relatively strong covalent bond in Nb OF_2, thus weakening the transverse vibration of F and O in Nb OF_2, compared with the case of Nb F_3.In this study, we proposed a way to tailor negative thermal expansion of metal fluorides by introducing the oxygen atoms.The present work not only predicts two NTE compounds, but also provides an insight on thermal expansion control by designing chemical bond type. |
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| Keywords: | negative thermal expansion fluorides lattice dynamics calculation average atomic volume negative Grüneisen parameters |
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