The introduction of phosphonium cations increases the ferroelastic phase transition temperature of [(CH3)3PCH2CH2CH3]2(n-C4H9NH3)Bi2Br9 to above room temperature.

The remarkable material stability and structural diversity of two-dimensional (2D) organic-inorganic hybrid perovskites (OIHPs) constitute a vast available library of versatile materials. In particular, ferroelastic property, for which the spontaneous strain can be transformed by applying mechanical stress, is very promising for extensive nanotechnological applications. However, integrating ferroelastic property into 2D OIHPs is still in its infancy. Herein, we designed two new 2D OIHPs (C 3 H 5 CH 2 NH 3 ) 2 [MCl 4 ] (M=Mn for 1 and Cd for 2), which undergo reversible ferroelastic phase transitions with an Aizu expression 4/mmmFmmm. The templating influence of the more distorted inorganic framework on the disordering of organic cations and the stronger hydrogen bonds has a key role in the striking improvement of Curie temperature from 246 K in 1 to 273 K in 2. Meanwhile, the minimized alteration of structural motif ensures the well maintaining of the ferroelastic performance in the forms of crystals and thin films, as demonstrated by the identifiable evolution of domain structures. This work will provide a fertile new ground for enlarging the limited number of 2D ferroelastic OIHPs with better practical utility.

Ferroelastic materials have received special attention because of their great promise for mechanical switches, piezoelectric sensors, and data storage applications. Here, we report a novel ferroelastic semiconducting hybrid organic–inorganic perovskite (C3H7N2S)PbBr3 (1) [(C3H7N2S)+ is 2-amino-2-thiazolinium] with a ferroelastic phase transition at 395 K and an optical band gap of 3.43 eV. 1 has a one-dimensional BaNiO3-type structure and undergoes a high-temperature ferroelastic phase transition with an Aizu notation of mmmF2/m. Meanwhile, 1 exhibits dielectric switch near the phase transition temperature. By introducing the thioether group, the motion of the molecules or ions of 1 is hindered after the sorption of Pd(II) metal ions, which leads to the disappearance of the high-temperature ferroelastic phase transition and dielectric switch. This is the first reported ferroelastic semiconductor material with Pd(II) adsorption property, by studying the influence of Pd(II) adsorption on high-temperature ferroelastic phase transition, it may be enlightening to further uncover the mechanism of phase transition or the origin of ferroelasticity, which represents an important step toward multifunctional applications of lead-hybrid perovskite-based ferroelastic materials.

Hybrid perovskites with mixed organic cations have recently received extensive focus from researchers for their structural tunability, enhanced performance, and stability. However, because there are certain requirements for the size of different organic cations to form hybrid perovskites with mixed organic cations, reports on hybrid perovskites that can contain both phosphonium and ammonium cations have been rare. Here, we report an organic–inorganic hybrid perovskite (Me3PCH2CH2CH3)2(CH3CH2CH2NH3)Sb2Br9 (1) with [Me3PCH2CH2CH3]+ cations and [CH3CH2CH2NH3]+ cations. Compound 1 exhibits a reversible phase transition at 371.3/353.2 K. Compared with the organic–inorganic hybrid perovskites only with [Me3PCH2CH2CH3]+ cations or [CH3CH2CH2NH3]+ cations, the phase transition temperature of the organic–inorganic hybrid perovskite formed by mixing [Me3PCH2CH2CH3]+ cations and [CH3CH2CH2NH3]+ cations is significantly increased, and the thermal stability is improved. Structural analysis shows the disorder of [CH3CH2CH2NH3]+ cations and the twisting motion of [Me3PCH2CH2CH3]+ cations and the inorganic skeleton are the major reasons for the phase transition of 1 at high temperatures. Furthermore, 1 possesses semiconductor properties with an optical band gap of 2.945 eV. This discovery will shed light on exploring more excellent functional perovskite materials with mixed organic cations.

In this work, we have obtained a hybrid organic–inorganic ABX3-type compound. It undergoes two phase transitions and displays semiconducting properties. And it has the ability to absorb Pd(ii) ions due to the presence of thioether groups.

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