Accession Number : AD0689622

Title :   THEORETISCHE EN EXPERIMENTELE STUDIE VAN DE JAHN-TELLER VERVORMDE PEROWSKIETSTRUKTUUR (Theoretical and Experimental Study of the Jahn-Teller Deformed Perovskite Structure),

Corporate Author : GHENT RIJKSUNIVERSITEIT (BELGIUM) NATURAL SCIENCE LAB

Personal Author(s) : Iserentant,Christine M.

Report Date : 1968

Pagination or Media Count : 94

Abstract : An approximate model was constructed based on the pairwise interaction of neighboring Jahn-Teller distorted Mn(3+)O6-complexes. The configurational energy of the model was derived in terms of occupation variables, and has been used to deduce the structure of the distorted phase which results from an ordering of the octahedra at low temperatures. At high temperatures, where the thermal agitation dominates, a statistically cubic structure appears. Using methods of statistical mechanics expressions for the principal thermodynamic functions have been derived. An adequate approximation for the temperature dependence of the lattice parameters has also been deduced. The obtained results imply the possibility to generalize the theory by taking into account composition dependence and the simultaneous presence of different kinds of Jahn-Teller active or inactive ions. In the experimental part of this work the discussion of the preparation of a number of ((1 -- x) La, xCa) MnO3 compounds shows the great influence of the firing conditions on the composition. Chemical analysis yields the percentage Mn(4+)-ions present in the specimens of which the cell dimensions are determined by X-ray analysis. From thermal dilatation measurements the behaviour of the compounds during phase transformations is investigated. (Author)

Descriptors :   (*PEROVSKITES, *CRYSTAL STRUCTURE), CALCIUM COMPOUNDS, LANTHANUM COMPOUNDS, MANGANESE COMPOUNDS, FERROELECTRIC CRYSTALS, PHASE STUDIES, THERMAL STABILITY, MATHEMATICAL ANALYSIS, BELGIUM

Subject Categories : Crystallography
      Solid State Physics

Distribution Statement : APPROVED FOR PUBLIC RELEASE