The layered perovskites (C₃H₇NH₃)₂MnCl₄(PAMC) and (C₂H₅NH₃)₂MnCl₄(EAMC): birefringence studies and the symmetry of the commensurately modulated ε phase of PAMC

Abstract

INFORMATION THEORY AS A BASIS FOR THE MAXIMUM DETERMINANTstructure-factor magnitudes are obtained from experiment. Nevertheless, the extrapolation of data, in both cases, corresponds to determination of an analytic function whose squared modulus is a function of maximum entropy measure. The definition for entropy measure is that given by Ponsonby (1973), parallel form and shown to be equivalent. With only the restrictions that (electron) density be positive, and that matrices and determinants be of small enough order to be positive definite, the two equivalent formulations yield identical results and provide an informationtheoretic interpretation of the maximum determinant.v V being the unit-cell volume. Ponsonby emphasizes that this is strictly only a measure of relative entropy of the real power spectrum of an underlying signal. In this sense maximum H' corresponds to maximum entropy measure p(r) = Ig(r)l z, and a maximum-entropy distribution function for Gh, the transform of g(r). Equation (6) AbstractBy measuring the birefringence on (001) platelets of PAMC as a function of temperature, previously determined phase transitions have been confirmed. Large effects were measured on passing through the normal-incommensurate ~ --, y transition and through the normal-commensurate ~ --, e transition, whereas the commensurate-normal e--, 6 and the incommen-* Bis(n-propylammonium) tetrachloromanganate.

Re-entrant phase transition of the crystalline ion conductor Ag7P3S11

“…Re-entrant phenomena are frequently found in liquid crystalline and lyotrophic systems [1][2][3], whereas they have been rarely observed in the crystalline state [4][5][6][7]. Here we are reporting this phenomenon in the crystalline ion conductor Ag 7 P 3 S 11 .…”

Raman spectroscopic study of structural phase transitions in the layer crystals (EtNH3)2MCl4with M=Cd and Mn

“…The structural phase transitions of EAMnC and EACdC have been studied by NMR (Blinc eta1 1977), crystallographic (Chapuis 1977, Depmeier 1977, Depmeier and Heger 1978, optical (Brunskill andDepmeier 1982, Karajamaki eta1 1981): dielectric , calorimetric (Tello et a1 1977) and infrared (Oxton 1979, Peyrard andPerret 1979) measurements. They are summarised in table 1.…”

Study of the modulated phase of (C3H7NH3)2CdCl4 by single-crystal X-ray diffraction

“…X-ray and neutron investigations (Brunskill & Depmeier, 1982;Depmeier & Mason, 1982, 1983 revealed the presence of the so-called e phase which has strong analogies with the INC phase of (C3HTNH3)2CdC14. This phase has the P sr l (0,/3,0), with fl = 1 + 6. same superspace group Abma…”