Understanding ferroelectricity is of both fundamental and technological importance to further stimulate the development of new materials designs and manipulations. Here, we perform an in-depth first-principle study on the well-known ferroelectric barium titanate BaTiO$_{3}$ under a hydrostatic negative pressure, showing an isosymmetric phase transition to a supertetragonal phase with high $c/a$ ratio of $\sim1.3$. The microscopic origin and driving mechanisms of this phase transition are identified as a drastic change of the covalently $π$-bonded electrons. These findings provide guidance in the search for new supertetragonal phases, with great opportunities for novel multiferroic materials; and can be generalized in the understanding of other isosymmetric phase transitions.
Origin of the large phonon band-gap in SrTiO3 and the vibrational signatures of ferroelectricity in ATiO3 perovskite: First principles lattice dynamics and inelastic neutron scattering of PbTiO3, BaTiO3 and SrTiO3
Local structural origins of the distinct electronic properties of Nb-substituted SrTiO$_3$ and BaTi$O_3$
在钙钛矿SrTiO $_3$中的Ti位点上接近或小于10%的Nb取代导致金属行为，这与在BaTiO $_3$中所看到的相反。由于两种材料的结构和电子数几乎相同，低取代的不同基态一直是一个长期存在的难题。在这里，我们从平均和局部结构的中子研究中发现，我们认为这些微妙而关键的差异支撑着这些迷人材料中独特的电子特性。而SrTi $_{0.875}$ Nb_ ${0.125}$ O $_3$在15 K下具有畸变的非立方结构，结构中的BO $_6$八面体是规则的。另一方面，BaTi $_{0.875}$ Nb $_{0.125}$ O $_3$显示出局部阳离子偏心同时保持立方结构的证据。
