The Raman spectra of (CH3),NMnC13 (TMMC) and (CH3),NCdCI3 OMCC) single crystals have been studied at different pressures between 0 and 6 kbar and at temperatures ranging from 80 to 300 K. The P , T phase diagrams of TMMC and TMCC have been determined, and a generalized phase diagram for these systems is proposed. This diagram includes four different structural modificiations whose structures are discussed on the basis of the present Raman results and of previously published structural data. Phase 1 is hexagonal (P6,/m, Z = 2 space group) and exhibits orientational disorder of the (CH3)4Nf groups; phases 11,111 and IV are monoclinic and apparently ordered. Phase 111 (P2,/rn, Z = 2) exhibits a re-entrant character. The Raman spectra of phase I1 are consistent with the P2,/a, 2 = 4 space group induced by anti-phase translations of the octahedra chains, but do not reveal any feature that could be related to an incommensurability. It is concluded that the structure of phase IV is very complex (for instance P2,/rn, Z = 8 or P2,/a, Z = 12). The orderdisorder processes and their possible coupling with other lattice dynamic properties are considered, to explain the 10 I1 and l o 111 transitions; additional structural information is needed in order to choose between the different models examined.

The Raman spectra (0 to 1000 cm−1) of the isostructural compounds (CH3)4NMnCl3 (TMMC), (CD3)4NMnCl3 (d‐TMMC) and (CH3)4NCdCl3 (TMCC) are recorded at different temperatures (from 25 to 300 K) and analysed in view of the previously reported structural data and phases transitions. The order‐disorder monoclinic‐hexagonal phase transition occurring at 126 K in TMMC and d‐TMMC is characterized in particular by the appearance, in the hexagonal disordered phase, of a diffuse scattering centered at ω = 0, due to the “rotatory” mode of the MCl3 chains coupled with a (CH3)4N+ ion (TMA) overdamped libration. In TMCC two transitions occur at 118 and 104 K. The mechanism for the monoclinic‐hexagonal transformation at 118 K is probably related to a change in the TMA ion configuration. Furthermore, the observed Raman spectra give some evidence for the existence of a new disordered state of the TMA ions in this intermediate phase. The transition at 104 K is then related to a complete ordering of the TMA ions.

No abstract

No abstract

The influence of heat treatment on the appearance and the evolution of the space charge repartition within an epoxy resin polymer material is investigated. The space charge measurements were made using the thermal step method (TSM) and the thermally stimulated depolarization currents (TSDC) method. The results obtained show the behaviour of the space charge density after heat treatment and, in particular, it can be concluded that the charges are stabilized in deep levels.© 2001 Society of Chemical Industry