NEUTRON-DIFFRACTION STUDY OF THE STRUCTURAL PHASE-TRANSITION IN LITHIUM AND VANADIUM SUBSTITUTED COPPER FERRITE

The neutron diffraction method in real time (RTND) is applied to study the structural phase transition in CuLi0.1V0.1Fe1.8O4. Both on heatin g to 740 K and on cooling the sample a reversible structural transitio n is observed from the tetragonal phase to the cubic one and reversely , with a hysteresis of about 50 K. The parameter of the spinel inversi on considerably decreases on heating and recovers on cooling. Moreover , Debye-Waller factors of atoms at the A and B sites in the spinel str ucture abruptly change at the phase transition. In the tetragonal phas e a pronounced dispersion of lattice parameters is observed due to loc al fluctuations of the spinel degree of inversion. The obtained result s permit to interpret the phase transition as being of diffusion type related to the achievement of critical temperature and critical concen tration of copper cations in the B sites of the elementary cell.