NH_(+)^(4)/K^(+)-substitution-induced C–F–K coordination bonds for designing the highest-temperature hybrid halide double perovskite ferroelastic

Ferroelastic materials with switchable spontaneous strain possess widely potential applications in the field of energy and information conversion.Recently,organic-inorganic hybrid halide double perovskites (OIHHDPs) have become a charming new platform for developing various functional materials,such as ferroelectrics,fluorescence and X–ray detection.Nevertheless,OIHHDP ferroelastic materials,especially high-temperature ones,are rare.Herein,we initially synthesized an OIHHDP ferroelastic,(2,2-difluoroethanamine)_(2)[(NH_(4))InCl_6](1),which possesses a ferroelastic phase transition at 407 K.Moreover,thanks to the flexible B-site for OIHHDPs,we replaced the NH_(4)^(+) ions within[(NH_(4))InCl_6]_n^(2n–)formworks with K^(+)ions,which endows with coordination bonds between 2,2-difluoroethanamine organic cations and[KInCl_6]_n^(2n–)formworks.Due to the existence of coordination bonds,the phase transition temperature of (2,2-difluoroethanamine)_(2)[KInCl_6](2) can reach 458 K.As far as we know,this value is the highest reported in OIHHDP ferroelastics.This work offers inspiration for the design of high-temperature OIHHDP phase transition materials including ferroelectrics and ferroelastics.

Enantiomeric hybrid high-temperature multiaxial ferroelectrics with a narrow bandgap and high piezoelectricity

Ferroelectric semiconductors have sparked growing attention in the field of optoelectronics,due to their unique ferroelectric photovoltaic effect.Recently,substantial efforts have been devoted to the development of ferroelectric semiconductors,including inorganic oxides,organic-inorganic hybrids,and metal-free perovskites.Nevertheless,reports of ferroelectric semiconductors with a bandgap of less than 2 eV have been scarce.Here,in combination with the incorporation of triiodide(I_(3)−)and the introduction of chiral cations,we successfully constructed a pair of enantiomeric organic-inorganic hybrid ferroelectric semiconductors,(S-1,2-DAP·I)_(4)·I_(3)·BiI_(6)and(R-1,2-DAP·I)_(4)·I_(3)·BiI_(6)(R/S-1,2-DAP=(R/S)-(–)-1,2-diaminopropane),which possess high-temperature multiaxial ferroelectric phase transition with an Aizu notation of 422F2(s)at 405 K,a narrow bandgap of 1.56 eV comparable to that of CH3NH3PbI_(3)(∼1.5 eV),and an impressive piezoelectric response(piezoelectric coefficient,d22 of 35 pC/N)on par with PVDF(polyvinylidene fluoride,30 pC/N).With intriguing attributes,(S-1,2-DAP·I)_(4)·I_(3)·BiI_(6)and(R-1,2-DAP·I)_(4)·I_(3)·BiI_(6)exhibit great potential for application of self-power polarized-light detection and piezoelectric sensors.

Deuteration triggered downward shift of dielectric phase transition temperature in a hydrogen-bonded molecular crystal

Deuteration of hydrogen-bonded phase transition crystals can increase the transition temperatures due to the isotope effect. But rare examples show the opposite trend that originates from the structural changes of the hydrogen bond, known as the geometric H/D isotope effect. Herein, we report an organic crystal, diethylammonium hydrogen 1,4-terephthalate, exhibits a reversible structural phase transition and dielectric switching. Structural study shows the cations reside in channels formed by one-dimensional hydrogen-bonded anionic chains and undergo an order-disorder transition at around 206 K. The deuterated counterpart shows an elongation of the O…O hydrogen bond by about 0.005 A. This geometric isotope effect releases the internal pressure of the anionic host on the cation guests and results in a downward shift of the phase transition temperature by 10 K.