BREAKDOWN OF THE ANTIFERRODISTORSION JAHN -TELLER ORDERING IN KDY(MOO4)(2) CRYSTAL IN MAGNETIC-FIELD - THE INTERMEDIATE PHASE-FORMATION

The layered crystal KDy(MoO4)(2) has been investigated by means of pol arization optics in the wavelength region 400-800 nm and in the extern al magnetic field applied along the direction of the maximum g-factor of the sites of one of the sublattices. A new field-induced structural phase transition was revealed at the temperature 7 K in the field H-1 = 32 kOe. The mutual transformations between low- and high-temperatur e phases occur through a formation of the intermediate phase. It is su pposed that intermediate phase has a modulated structure. The extrapol ated temperature dependences of the transition fields H-1 and H-2 show n that the intermediate crystal phase has to exist at H = 0 in the tem perature range from T-1 = 11.5 K to T-2 = 14.3 K as well.