Theoretical prediction of piezoelectric property of new LiNbO 3 -type compound AlTlO 3
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.92
Theoretical prediction of piezoelectric property of new LiNbO3-type compound AlTlO3 Kaoru Nakamura1 and Toshiharu Ohnuma1 1
Central Research Institute of Electric Power Industry, 2-6-1, Nagasaka, Yokosuka, Kanagawa, Japan
ABSTRACT
By using systematic first-principles calculation, we found that AlTlO3 compound of LiNbO3 structure shows large piezoelectric constants e33 of 10.7 C/m2 and d33 of 56.7 pC/N. These piezoelectric constants are approximately six times larger than those of LiNbO3. AlTlO3 is predicted to be stabilized above 7 GPa. On the other hand, the calculated dielectric constant H33 shows diverged behavior around 2 GPa. This result indicates that AlTlO3 can be quenchable. Decomposition of the predicted piezoelectric constant revealed that the large piezoelectricity of AlTlO3 originates from the Tl displacement in accordance with external perturbation, which drives the ferroelectric soft mode of the corresponding paraelectric phase. However, the energy difference between the ferroelectric and paraelectric phases was small, approximately 1 meV/f.u. These insights suggest that fluctuation between ferroelectric and paraelectric phases causes large piezoelectricity in AlTlO3.
INTRODUCTION LiNbO3 (LN) structure, belonging to the space group of R3c, is closely related to the perovskite structure [1]. In this structure, LiO6 and NbO6 polyhedron are largely rotated with respect to the cubic perovskite structure. Deformation path between cubic perovskite structure and LN structure can be found_ from the unstable phonon eigenvector of cubic phase, R25 soft mode, which results in R3c paraelectric phase [2]. Ferroelectric transition from paraelectric phase of *15 mode results in ferroelectric R3c phase [3]. Due to the different bonding nature between Li–O and Nb–O, the atomic positions of Li and Nb are off-centered within oxygen layers along C-axis. This structural characteristic is the ferroelectric nature of LiNbO3. One of the notable properties of LiNbO3 is its high Curie temperature (~1400 K [4]). However, the piezoelectric properties of LiNbO3 are not significantly superior than those of Pb-based complex perovskites. Based on the notion of morphotropic phase boundary [5], large piezoelectricity occurs at the expense
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of phase stability. Therefore, thermodynamic stability and piezoelectricity must have a trade-off in general. So far, many compounds were found to form LN-type structure under highpressure condition, and some of them were in the quenchable phase. For example, LNtype ZnSbO3 was successfully synthesized under high pressure [6], and its spontaneous polarization was investigated by first-principles simulation [7]. On the other hand, highpressure phase of LiNbO3 itself revealed no pie
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