Halogen substitution effects on optical and electrical properties in 3D molecular perovskites

Abstract

In 1 the SHG effect was observed, and remarkably 2 represents the first 3D ferroelastic material characterized by two ferroelastic phases.

A Three-Dimensional Molecular Perovskite Ferroelastic with Two-Step Switching of Quadratic Nonlinear Optical Properties Tuned by Molecular Chiral Design

“…6−8 However, unlike ferromagnetics and ferroelectrics, there are relatively rare reports about molecular ferroelastics with three-dimensional (3D) perovskite structures. 9,10 It remains difficult to find and design molecular ferroelastics, because it must belong to one of the 94 species of the ferroelastics phase transition defined by Aizu. 11 Physicists have discovered and researched a large number of inorganic ferroelastic materials.…”

“…Ferroelastic materials, as a class of ferroic materials, have drawn tremendous attention owing to manifold technical applications, such as sensing, information storage, superelasticity, and mechanical switches. − Its crystal possesses two or more orientation states in the absence of mechanical stress and can switch or control from one to another of these states by means of an external stress field. − However, unlike ferromagnetics and ferroelectrics, there are relatively rare reports about molecular ferroelastics with three-dimensional (3D) perovskite structures. , It remains difficult to find and design molecular ferroelastics, because it must belong to one of the 94 species of the ferroelastics phase transition defined by Aizu …”

Tilts and shifts in molecular perovskites

“…1 exhibits a tilt angle of 45°along one axis. 37 The in-phase tilt (M 2 + ) is also relatively common in dicyanamides and formates, although not quite as markedly. In contrast, these two modes are scarce in azide perovskites and when present, they are less pronounced relative to the other active distortions.…”

“…By way of example, the high-temperature Cmce phase of [Et 3 PIJCH 2 ) 2 F]CdijNIJCN) 2 ] 3 is isostructural to [(CH 3 ) 2 NH 2 ]MnIJN 3 ) 3 at ambient conditions, but distinct from the Cmce phase of [Et 3 PPr]CdijNIJCN) 2 ] 3 (Et = ethyl, Pr = propyl). 13,37,55 Likewise, the Ibam symmetries of [Et 3 PPr]CdijNIJCN) 2 ] 3 and [NPr 4 ]FeijNIJCN) 2 ] 3 arise from different distortion modes and these systems are therefore not isostructural. 55,56 However, the Ibam and Cmce phases of [Et 3 PPr]CdijNIJCN) 2 ] 3 presented in ref.…”

“…1]. 7,9,16,37,40,47,57,58 This structure features out-of-phase tilts (R 5 − ) of equal amplitude polarised along two axes of the perovskite unit cell and another out-of-phase tilt of different magnitude along the third direction (a − a − b − in Glazer notation). 24 Yet, the tiltdriven C2/c phase is the only structure appearing in all different families, and such common phases seem to be more of an exception than a rule.…”