Wulf Depmeier

High-temperature solution growth of Pb(Fe0.5Nb0.5)O3 and Pb(Mn0.5Nb0.5)O3 crystals

Abstract High-temperature solution growth of the ferroelectric crystals Pb(Fe0.5Nb0.5)O3 and Pb(Mn0.5Nb0.5)O3 with and without application of the accelerated crucible rotation technique (ACRT) is described. The dimensions of the crystals allow, for the first time, optically-controlled measurements on ferroelectric single domains, and preliminary observations on Pb(Fe0.5Nb0.5)O3 are reported.

The Role of Some Cage Ion Substitutions for the Phase-Transition Characteristics of Aluminate Sodalites

The system CaxSr8-x[Al12O24](WO4)2 has been studied with the view or elucidating the role of cage cation substitution on the phase transition behaviour. Room temperature Guinier photographs show splitting and extra reflections indicating structural variations from orthorhombic through tetragonal to cubic symmetry. DSC measurements were made to detect the changes in transition temperature and in heat of transition. Mixing of Ca and Sr lowers the transition temperatures from above 300°C for the end members, down to room temperature, where a vast range of cubic members exists.

Incommensurate phases in PAMC: where are we now?

Abstract A survey is given of the particularities of the incommensurately modulated phases of PAMC (= (n-C3H7NH3)2 MnCl4), especially as the experimental situation is concerned. The theoretical results are also briefly mentioned. Difficulties which occur in some experiments are outlined and proposals for a number of future experiments are made.

Structure Refinement of Trigonal Iron–Chlorine Boracite

Fe3B7O13Cl is rhombohedral, space group R3c, with ahex 8.6231(5), and chex 21.0503(5) A, Z = 6; and arh 8.6035(7) A, αrh 60.15(1)°; dc = 3.576. The final R = 0.038 (Rw = 0.054) for 1544 reflections. Bond lengths and bond angles do not differ significantly from, but are more accurate than, those reported for isostructural Fe2.4Mg0.6B7O13Cl (Dowty and Clark (1973). At. coordinates are given.

Aluminate-Sodalite Sr8(Al12o24)(Cro4)2 - a New Ferroelectric Material

On flux grown polydomain single crystals of Sr8[Al12O24] (CrO4)2 exploratory domain studies and measurements of birefringence, polarization, dielectric constant and transition enthalpy demonstrate the existence of a first order ferroelectric phase transition at about 2954↓-299↑K.

Structure of Cubic Aluminate Sodalite, Sr8[Al12o24](Cro4)2

The title compd. is cubic, space group I.hivin.43m, with a 9.427(2) .ANG.; dc = 3.25 for Z = 1. The final R = 0.045 for 256 reflections. The at. coordinates are given. The sodalite framework is (almost) fully expanded, therefore space group Im.hivin.3m is also possible. The corresponding refinement gave results almost identical with that in I.hivin.43m (R = 0.048 for 149 reflections). The tetrahedral CrO4 cage anion is 6-fold disordered; only the superposition corresponds to cubic symmetry.

Vibrational spectra of perovskite-type layer compounds. Bis(propylammonium) tetrachloromanganate and -cadmate

Abstract Infrared spectra of the phases of (PrNH 3 ) 2 MnCl 4 and (PrNH 3 ) 2 CdCl 4 occurring at room temperature and below have been measured and are discussed in terms of the structural characteristics of the salts. The lowest-temperature phase of the cadmium salt was found to possess an unusually complex spectrum and possible reasons for this are suggested.

Structure of boracite Cu3B7O13I

Cu3B7O13I is cubic, space group F43c, with a 12.0203(7) A; d.(calcd.) = 4.608 for Z = 8. Final R = 0.014 for 110 unique reflections. At. parameters are given. This new boracite has been prepared by high-pressure synthesis; its structure is comparable with that of other cubic boracites. No structural phase transition could be observed between 15 and 1265 K.

An application of the flux function method to a five-component system: The chemical vapour transport of Ni-Cl boracite

Abstract The flux function method has been applied to the five-component Ni/BO/Cl/H system to find promising conditions for the growth of Ni-Cl boracite crystals by chemical vapour transport.

PdB2O4, the first palladium borate

PdB2O4 were prepd. from a 1:1 mixt. of Pd(NO3)2.2H2O and B2O3 at 40 kbar and 800 Deg. PdB2O4 belongs to space group I.hivin.42 d with a 11.675(5) and c 5.703(5) .ANG., Z = 12, and d. (calcd.) = 4.92 Mg/m3.