| Ferroic materials have been widely used as functional materials in the modern electronic field,due to their rich physical properties,such as ferroelectricity,ferromagnetism,ferroelasticity,piezoelectricity and pyroelectricity.The conventional ferroic materials are mainly inorganic ceramics,such as barium titanate(Ba Ti O3),bismuth ferrite(BiFe O3),bismuth vanadate(BiVO4)and lead zirconate titanate(PZT).However,ferroic materials should be lightweight,flexible,easy to process and bio-friendly.These requirements are a challenge to conventional ferroic materials,because inorganic ceramics often require high-temperature sintering during the preparation process,and the finished products lack mechanical flexibility as well as are not easy to process.Although organic-inorganic hybrid lead-based halide perovskites with excellent photoelectric properties,structurally tunable and solvent-processing have partly overcome the problems faced by inorganic ceramic ferroic materials,the toxicity of lead element is still a worrying problem.In this context,organic-inorganic hybrid double perovskites have become a very attractive new platform for the development of ferroic materials,due to their non-toxicity and stability.However,currently reported organic-inorganic hybrid double perovskite ferroic materials still have the following shortcomings:(1)the Curie temperature(Tc)of ferroelastics is generally lower than room temperature,which limits their practical application;(2)The type of two-dimensional halide double perovskite ferroelectrics is single.Currently reported combinations of B?B?X sites only have Ag BiBr,and other suitable ion combinations have not been explored;(3)ferroic materials with satisfactory piezoelectric response are lacking;(4)Multifunctional ferroic materials still are lacking.Therefore,the work carried out in this paper is as follows:(1)Two one-dimensional organic-inorganic hybrid halide double perovskite ferroelastics,(2,2-DFEA)2[(NH4)In Cl6]and(2,2-DFEA)2[KIn Cl6],were synthesized by a simple solution evaporation method.(2,2-DFEA)2[(NH4)In Cl6]possesses high Tc of 407 K and multiaxial ferroelasticity.Then,the part hydrogen bonds between 2,2-DFEA organic cations and the one-dimensional perovskite framework were replaced with coordination bonds by replacing NH4+ions in one-dimensional perovskite framework[(NH4)In Cl6]n2n-with K+ions.Stronger coordination bonds endow(2,2-DFEA)2[KIn Cl6]with a higher Tc(458 K)than that of(2,2-DFEA)2[(NH4)In Cl6].(2)An Ag BiI combination of two-dimensional organic-inorganic hybrid halide double perovskite ferroelectric,(4,4-DFPDD)4Ag BiI8,was synthesized,which exhibits excellent ferroelectricity including a high Tc up to 422 K and a large spontaneous polarization(Ps)of 10.5?C·cm-2.Moreover,(4,4-DFPDD)4Ag BiI8 also exhibits promising X-ray response with high sensitivity up to 188?C·Gy-1air·cm-2 at 50 V bias and a detection limit below 3.13?Gyair·s-1 at 50 V bias.(3)An Ag Sb I combination of two-dimensional organic-inorganic hybrid iodide double perovskite ferroelectric,(4,4-DFPDD)4Ag Sb I8,was synthesized,which possesses a high Tc of 414K,a large Ps of 9.6?C·cm-2,ferroelectric photovoltaic effect,and photostrictive effect.Moreover,(4,4-DFPDD)4Ag Sb I8 exhibits an impressive X-ray responsivity,with a sensitivity as high as 704.8?C·Gy-1air·cm-2 at 100 V bias and a detection limit is as low as 0.36?Gyair·s-1 at 10 V bias.(4)A pair of multifunctional three-dimensional organic-inorganic hybrid rare-earth nitrate perovskite ferroelectrics,[(R/S)-N-methyl-3-hydroxylquinuclidinium]2Rb Eu(NO3)6,were synthesized by introducing chirality into organic-inorganic hybrid rare-earth nitrate perovskites.The introduction of chirality induces multiaxial ferroelectricity and ferroelasticity of[(R/S)-N-methyl-3-hydroxylquinuclidinium]2Rb Eu(NO3)6.The coupling of multiaxial ferroelectricity and ferroelasticity endows[(R/S)-N-methyl-3-hydroxylquinuclidinium]2Rb Eu(NO3)6 with a large piezoelectric response,their piezoelectric constant(d33)reaching up to 103 and 101 p C·N-1,respectively.Moreover,[(R/S)-N-methyl-3-hydroxylquinuclidinium]2Rb Eu(NO3)6 exhibit photoluminescence properties,including high quantum yields(84.71%and 83.55%,respectively)and long fluorescence lifetimes(5.404 and 5.256 ms,respectively).Meanwhile,combined with the chirality and outstanding photoluminescence properties,[(R/S)-N-methyl-3-hydroxylquinuclidinium]2Rb Eu(NO3)6 exhibit circularly polarized luminescence.To a certain extent,this work has filed the gap of one-dimensional organic-inorganic hybrid halide double perovskite ferroelasticity,two-dimensional organic-inorganic hybrid double perovskite iodide ferroelectrics and multifunctional hybrid rare-earth double perovskites.A strategy to control Curie temperature of ferroic materials is developed,that is,to control Curie temperature of ferroic materials by adjusting interaction force between organic cations and perovskite skeleton.It is proved that Sb3+ions,which has been neglected before,can also construct two-dimensional hybrid double perovskite ferroelectrics with ideal photoelectric response. |
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