A premartensitic phase in KAlF4: neutron and X-ray scattering evidences

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Abstract
From elastic neutron scattering experiments, it is shown that the anomalies which have been recently observed in the high temperature phase of KAlF 4 by the X-ray mono-Laue technique can be attributed to embryonic domains of a premartensitic phase which coherently coexists with the high temperature phase. The arrangement of the domains and the lattice parameters of the premartensitic phase are determined. On the basis of geometrical considerations and with regard to the two-dimensional character of this layered compound we propose a possible structure for the premartensitic phase. The coexistence of the two phases can be interpreted by means of edge dislocations which are presumably formed during the crystal growth procedure. The role played by the premartensitic phase on the onset of the KAlF4 martensitic transformation is discussed