OVERCRITICAL TRACE OF AN ISOMORPHOUS PHASE-TRANSITION IN BETA-TB-2(MOO)(4) CRYSTALS

The paper presents spontaneous polarization, dielectric permittivity a nd thermal expansion coefficient for beta-Tb-2(MoO)(4) crystals (label ed later with TbMoO) in temperature range of 78-450 K. It was confirme d that a ferroelectric phase transition in this crystal is the first-o rder phase transition, however, close to that of the second-order. TbM oO physical properties investigated in this work can be described with in the ferroelectric transition by a two-component order parameter, ha ving treated this transition as the improper one. It was found that th e dielectric permittivity anomaly and dielectric loss tangent in the t emperature range of 120-320 K can be treated as an overcritical trace of an isostructural phase transition.