The specific heat of the ferroelectric phase transition in N(CH3)4CdBr3

The phase transition sequence in tetramethylammonium cadmium chloride (TMCC):

“…Table 2 summarizes the frequency assignments used to construct the harmonic specific heat. In general, the values assigned to TMCC are similar to those found for TMMC [5,8] and TMCB (see [16] and references therein, [23]), with only slight differences in the low part of the spectrum which are more pronounced for this last crystal. As expected, the frequencies associated with the bending and stretching modes of the Br-Cd bonding are smaller than in the case of Cl-Cd or Cl-Mn, as a result of the mass differences between the two halogen ions.…”

“…Earlier, the specific heat of the related crystals [N(CH 3 ) 4 ]MnCl 3 (TMMC) and [N(CH 3 ) 4 ]CdBr 3 (TMCB) was reported [12,[16][17][18][19]. In addition, specific heat data for TMCC and TMMC below 52 K were published in references [12] and [12,17,19] respectively.…”

“…The lattice harmonic contribution to the specific heat can be determined by means of the lattice mode frequencies obtained from Raman and infrared measurements on TMCC [5,8]. The frequencies of the inactive modes have been estimated from data obtained from related compounds [16,22].…”

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

“…[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. [18][19][20][21][22][23][24][25][26][27][28][29] The crystal structure at room temperature consists of isolated linear chains of face-sharing CdBr 6 octahedra separated by N(CH 3 ) 4 ions. N(CH 3 ) 4 CdBr 3 has two phase transition temperatures, 160 and 390 K, 19,22,23 with three phases denoted as III, II, and I, respectively, in the order of increasing temperature.…”