The specific heat of N(CH₃)₄MnBr₃by adiabatic calorimetry

Abstract

The specific heat of N(CH 3 ) 4 MnBr 3 has been measured by adiabatic calorimetry, using both static and dynamic methods. The obtained results have permitted the calorimetric characterization of the phase transition which the crystal shows at 143 K. The comparison with other compounds of the family has been used to generate an adequate baseline for the normal lattice contribution to the specific heat. These results allow for an accurate estimation of the phase transition thermodynamic functions: H = 218 R K and S = 1.58 R. The calorimetric data are very close to those found for the isomorphous N(CH 3 ) 4 CdBr 3 and suggest a similar frequency spectrum for the lattice vibrational modes and the anharmonic contributions to the specific heat.

NMR analysis of structural geometry and molecular dynamics in perovskite-type N(CH3)4CdBr3 crystal near high-temperature phase transition

“…In a previous study, the 1 H nuclear magnetic resonance (NMR) spin-lattice relaxation time T 1 in the laboratory frame did not reveal any anomaly in the temperature range of 77-400 K for N(CH 3 ) 4 CdBr 3 . 18 This phenomenon can be explained by the relaxation mechanism owing to the fast reorientation of the CH 3 groups.…”

“…To minimize the spinning sideband, the MAS speed was measured at 10 kHz. 1 H and 13 C chemical shis were recorded using tetramethylsilane as the standard. The one-dimensional (1D) NMR spectra of 1 H and 13 C were obtained with a delay time of 0.5 s. The 1 H and 13 C spin-lattice relaxation times in the rotating system (T 1r ) were measured with delay times from 200 ms to 100 ms; a 90°pulse was used for acquiring 1 H and 13 C data, with a delay of 3.6-3.8 ms.…”

“…Structural analysis was performed by monitoring 1 H in N(CH 3 ) 4 CdBr 3 using MAS NMR at increasing temperatures. The temperature-dependences of the 1 H NMR chemical shis and linewidths are shown in Fig.…”

“…ABX 3 perovskites are an interesting group of compounds that undergo phase transition accompanied by remarkable changes in their physical and chemical properties. [1][2][3][4][5][6][7] Many studies on organic-inorganic hybrid compounds have yielded meaningful results because of the wide applicability of these materials. [8][9][10][11][12][13][14][15][16][17] Tetramethylammonium tribromocadmate (N(CH 3 ) 4 CdBr 3 ) belongs to the N(CH 3 ) 4 BX 3 (B = 55 Mn, 59 Co, 64 Cu, 65 Zn, 113 Cd; X = 35 Cl or 79 Br) family of ABX 3 -type perovskites.…”