Target Designing Phase Transition Materials through Halogen Substitution

Abstract

Crystalline materials have received extensive attention due to their extraordinary physical and chemical properties. Among them, phase transition materials have attracted great attention in the fields of photovoltaic, switchable dielectric devices, and ferroelectric memories, etc. However, many of them suffer from low phase transition temperatures, which limits their practical application. In this work, we systematically designed crystalline materials, (TMXM) 2 PtCl 6 (X = F, Cl, Br, I) through halogen substitution on the cations, aiming to improving phase transition temperature. The resulting phase transition of (TMXM) 2 PtCl 6 (X = F, Cl, Br, I) get a significant enhancement, compared to the parent compound [(CH 3 ) 4 N] 2 PtCl 6 ((TM) 2 PtCl 6 ). Such phase transition temperature enhancement can be attributed to the introduction of halogen atoms that increase the potential energy barrier of the cation rotation. In addition, (TMBM) 2 PtCl 6 and (TMIM) 2 PtCl 6 have a low symmetry and crystallize in the space group C 2 /c and P2 1 2 1 2 1 , respectively. This work highlights the halogen substitution in designing crystal materials with high phase transition temperature.

H/F Substitution Achieved Enantiomeric Organic Inorganic Hybrid Perovskites and Trigonal Structure [DMFP]3(CdBr3)(CdBr4)

“…In Figure c, the reversible phase transition of [DMFP] 3 (CdBr 3 )­(CdBr 4 ) was dominated by an exothermic peak at 413 K and an endothermic peak at 407 K. The entropy change value Δ S for the heating process is calculated to be 3.95 J mol –1 K –1 and the N value is calculated to be 1.61. The N values of hybrid perovskites and in this work are comparable to that of the order–disorder phase transition of OIHPs, such as (isoamylammonium) 2 PbCl 4 , ( N , N , N -trimethyl- tert -butylammonium)­CdCl 3 , (TMIM) 2 PtCl 6 , ( R )-, ( S )-, and (rac)-( N , N -dimethyl-3-fluoropyrrolidinium) CdCl 3 . In addition, the thermal gravimetric analysis (TGA) measurements of ( R )- or ( S )-[DMFP]­[CdBr 3 ], [DMFP] 3 (CdBr 3 )­(CdBr 4 ), and [DMP]­[CdBr 3 ] show their decomposition points are around 625, 624, and 675 K, respectively, indicating decent thermal stability (Figure S3, Supporting Information).…”

“…In Figure 1c, the reversible phase transition of [DMFP] 3 (CdBr 3 )(CdBr 4 ) was dominated by an exothermic peak at 413 K and an endothermic peak at 407 K. The entropy change value ΔS for the heating process is calculated to be 3.95 J mol −1 K −1 and the N value is calculated to be 1.61. The N values of hybrid perovskites and in this work are comparable to that of the order−disorder phase transition of OIHPs, such as (isoamylammonium) 2 PbCl 4 , 34 (N,N,N-trimethyl-tertbutylammonium)CdCl 3 , 35 (TMIM) 2 PtCl 6 , 36 [DMFP] 3 (CdBr 3 )(CdBr 4 ) match well with the simulated ones, which suggests their high phase purity, see Figure S6, Supporting Information. Figure 2a shows the PXRD curves of [DMP][CdBr 3 ].…”

Renewing Halogen Substitution Strategy for the Rational Design of High‐Curie Temperature Metal‐Free Molecular Antiferroelectrics

“…As the p ‐site atom of phenethylammonium cation is substituted from H to Br, the T c values have been greatly enhanced by ~160 K, changing from 322 K (for H‐PEAB) to 482 K (for Br‐PEAB). Generally, when the substituted atom becomes larger and heavier, the potential energy barrier of the tumbling motion of the organic cationic rotator increases, resulting in a higher temperature to induce the order‐disorder phase transition (Scheme 1c) [11] . This phenomenon is similar to that of the family of halogenated compounds [Me 3 NCH 2 X]PbI 3 (X=H, F, Cl, Br, I) [12] …”

Enhancing Phase Transition Temperature in Novel Crown Inclusion Materials through Anion‐Substitution Engineering

“…), forming a new crystal type. [1][2][3][4] Due to the rearrangement of microscopic particles (molecules, atoms or ions), the sample is often accompanied by changes with its physical properties (optical, electrical, magnetic properties and etc.) before and after the phase transition.…”

“…The essence of solid‐solid phase change is that the internal molecular arrangement and the crystal form of the sample changes under the stimulation of the external environment (temperature, light, force, etc. ), forming a new crystal type [1–4] . Due to the rearrangement of microscopic particles (molecules, atoms or ions), the sample is often accompanied by changes with its physical properties (optical, electrical, magnetic properties and etc.)…”