High-temperature structural phase transition in the LiCu2O2 multiferroic

The results of thermogravimetric, X-ray diffraction, and electrical studies of LiCu2O2 single crystals in the temperature range 300-1100 K are presented. A reversible first-order phase transition between the orthorhombic and tetragonal phases is found to occur in these single crystals at T = 993 K. A pronounced peak on a differential thermal analysis curve and jumps in the unit cell parameters and the electrical resistivity are detected at the phase-transition temperature. The data on the crystal structure of LiCu2O2 and the phase transition-induced change in the entropy determined in this work are used to conclude that the revealed phase transition is caused by the ordering-disordering of Li+ and Cu2+ cations in their structural positions.