Temperature- and pressure-dependent studies of a highly flexible and compressible perovskite-like cadmium dicyanamide framework templated with protonated tetrapropylamine. Issue 8 (8th February 2019)

• Record Type: Journal Article
• Authors: Mączka, Mirosław; Ptak, Maciej; Gągor, Anna; Sieradzki, Adam; Peksa, Paulina; Usevicius, Gediminas; Simenas, Mantas; Leite, Fabio Furtado; Paraguassu, Waldeci
• Is Part Of: Journal of materials chemistry. Volume 7:Issue 8(2019)
• Page Start: 2408
• Page End: 2420
• Publication Date: 2019-02-08
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c8tc06401f
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : Perovskite-like [TPrA][Cd(dca)3 ] undergoes four temperature-induced phase transitions associated with dielectric anomalies and one pressure-induced phase transition into a monoclinic phase. Abstract : We report temperature-dependent X-ray diffraction, thermal, dielectric, electron paramagnetic resonance (EPR), Raman and IR studies of [(C3 H7 )4 N][Cd(N(CN)2 )3 ] ([TPrA][Cd(dca)3 ]) exhibiting a rich sequence of temperature-induced phase transitions occurring at T 3 = 386 K, T 2 = 362 K, T 1 = 241 K and T 0 = 228 K. The X-ray diffraction study confirms the I 4/ mcm, P 4̄21 c and P 21 / n symmetry of the high-temperature phase, the phase stable between T 2 and T 1 and the low-temperature phase stable below T 0, respectively. Our data show that the driving forces for the phase transitions at T 3 and T 2 are the partial ordering of the tetrapropylammonium cations (TPrA + ) and dicyanamide (dca) linkers as well as the off-center shifts of TPrA + cations and the tilting of the CdN6 octahedra. X-ray diffraction data reveal that two low-temperature (LT) structural phase transitions at T 1 and T 0 are associated with strong monoclinic distortion of the [Cd(dca)3 ] − framework and further ordering of the TPrA + cations and dca linkers. Raman and EPR data confirm the strong distortion of the framework, while dielectric data are consistent with the partial ordering of the TPrA + cations at T 1 . Dielectric and Raman data also prove that the phase transition at T 0 is associated with further freezing of the propyl groups' motions of the TPrA + cations, whereas EPR data indicate that this phase transition is also associated with some distortion of the cadmium-dicyanamide framework. In the family of [TPrA][M(dca)3 ] compounds (M = Cd 2+, Mn 2+, Fe 2+, Co 2+, Ni 2+ ), phase transitions into monoclinic phases are unique only for the Cd analogue, and our data indicate that this behaviour can be attributed to the higher flexibility of the [TPrA][Cd(dca)3 ] framework compared to the other analogues. We also report high-pressure X-ray powder diffraction and Raman studies of [TPrA][Cd(dca)3 ]. Fitting of the pressure dependence of the unit cell volume to the third order Birch–Murnaghan equation of state gives a bulk modulus of 6.2(6) GPa and its pressure derivative B ′ = 12(2). The small value of the bulk modulus demonstrates the highly compressible nature of [TPrA][Cd(dca)3 ]. X-ray diffraction and Raman data show that this compound undergoes a pressure-induced phase transition between 0.3 and 0.4 GPa into a monoclinic structure, probably the same as that observed at ambient pressure below T 0 .