Stability and flexibility of heterometallic formate perovskites with the dimethylammonium cation: pressure-induced phase transitions

Abstract

We report the high-pressure Raman studies and DFT calculations of DMANaCr and DMAKCr perovskite formates.

Pressure-enhanced ferroelectric polarisation in a polar perovskite-like [C2H5NH3]Na0.5Cr0.5(HCOO)3metal–organic framework

“…In our previous high-pressure Raman studies of AmNaCr, DMANaCr and ImNaCr, we suggested that such large α parameters for the translational T'(Cr 3+ ) modes point to a strong compression of the CrO6 octahedral units. [27][28][29] Present highpressure diffraction data, however, allows us to calculate the volume of the NaO6 and CrO6 octahedra as a function of pressure (Fig. 5) using VESTA.…”

“…In addition, further variation can be achieved by replacing the divalent metal atoms with an equimolar mixture of alkali (M I =Na + or K + ) and trivalent metal ions (M III =Fe 3+ , Cr 3+ or Al 3+ ) to form double perovskites with the general formula AM I 0.5M III 0.5(HCOO)3. 11,[22][23][24][25][26][27][28][29][30] [C2H5NH2]Na0.5Fe0.5(HCOO)3 (EtANaFe) was the first polar and heterometallic formate MOF to be discovered, 22 and is one of the RT ferroelectric formate perovskites. 22,31 It crystallises in the polar monoclinic Pn space group at low-temperature (LT) and undergoes an order-disorder phase transition at 360 K to the nonpolar P21/n symmetry.…”

“…High-pressure XRD, IR and Raman experiments have previously been employed in studies of many formate-based MOFs. [27][28][29]31,[35][36][37][38][39][40][41][42][43][44] However, high-pressure crystal structures have been solved for a few formate frameworks only. 35,36,40,42,44 Among these compounds non-centrosymmetric high-pressure phases were reported for three crystals only; chiral [NH4]Zn(HCOO)3 and perovskite-like [(CH3)2NH2]M II (HCOO)3 (M II =Fe, Mn).…”

Effect of Alkali and Trivalent Metal Ions on the High-Pressure Phase Transition of [C2H5NH3]MI0.5MIII0.5(HCOO)3 (MI = Na, K and MIII = Cr, Al) Heterometallic Perovskites

“…This is similar to previous results for the DMA + cation, which showed the order DMAKCr > DMANaCr > DMAZn. 18 To our knowledge, the synthesis of EtAZn has not been reported, but assuming that it crystallizes in the same space group as the Mn compound ( Pna 2 1 ), 50 the HB energy is indeed calculated to be lower than for the three mixed metal compounds (0.66 eV, cf. Table S4 ).…”

“…Among the studied heterometallic MOFs with different protonated amines (ammonia, Am + ; imidazole, Im + ; dimethylamine, DMA + ; ethylamine, EtA + ; methylamine, MeA + , etc. ), 14 , 16 − 18 , 20 − 23 only a few exhibit structural ordering. Three analogues with the EtA + cation and Na + ions, EtANa 0.5 M III 0.5 (HCOO) 3 (M III = Al 3+ , Cr 3+ , Fe 3+ ), adopt monoclinic polar Pn symmetry with ordered EtA + cations in two independent sites ( Figure 1 a).…”