Extended Goldschmidt tolerance factor t is applied to the hybrid double perovskites (MA)2 [B'B''(CN)6 ] (MA=methylammonium cation) to predict and screen dielectric transitions in 121 compounds through the correlations among t, the radius of the B component rB and the transition temperature Tc , based on experimental results from model compounds. For (MA)2 [B'Co(CN)6 ], it is concluded that: i) when t>0.873, the cubic phase would be stable below 298 K; ii) when 0.873>t>0.805, the cubic phase would be stable between 298 and 523 K; iii) the larger the rB , the higher the Tc of the perovskite (Tc (1/2) ∝rB ); and iv) the Tc of the hybrid perovskites can be well tuned by doping the B components.

Deuteration of a hydrogen bond by replacing protium (H) with deuterium (D) can cause geometric changes in the hydrogen bond, known as the geometric H/D isotope effect (GIE). Understanding the GIEs on global structures and bulk properties is of great importance to study structure–property relationships of hydrogen-bonded systems. Here, we report a hydrogen-bonded host–guest crystal, imidazolium hydrogen terephthalate, that exemplifies striking GIEs on its hydrogen bonds, phases, and bulk dielectric transition property. Upon deuteration, the donor–acceptor distance in the O–H···O hydrogen bonds in the host structure is found to increase, which results in a change in the global hydrogen-bonded supramolecular structure and the emergence of a new phase (i.e., isotopic polymorphism). Consequently, the dynamics of the confined guest, which depend on the internal pressure exerted by the host framework, are substantially altered, showing a downward shift of the dielectric switching temperature.

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Extended Goldschmidt tolerance factor t is applied to the hybrid double perovskites (MA)2[B′B′′(CN)6] (MA=methylammonium cation) to predict and screen dielectric transitions in 121 compounds through the correlations among t, the radius of the B component rB and the transition temperature Tc, based on experimental results from model compounds. For (MA)2[B′Co(CN)6], it is concluded that: i) when t>0.873, the cubic phase would be stable below 298 K; ii) when 0.873>t>0.805, the cubic phase would be stable between 298 and 523 K; iii) the larger the rB, the higher the Tc of the perovskite (Tc1/2∝rB); and iv) the Tc of the hybrid perovskites can be well tuned by doping the B components.

No abstract