Effect of uniaxial pressure on the ferroelectric phase transition in Pb₅Ge₃)₁₁

Abstract

The effect of uniaxial pressure (X) up to 1 kbar, applied along the three main directions, on the Curie temperature and the dielectric constant ε c of a Pb 5 Ge 3 O 11 single crystal was investigated. The Curie temperature decreases with uniaxial pressure and the coefficient γ i (γ i ≡ ∂T c /∂(X i ) was determined as −6.5, −7.0 and −3.2 K kbar −1 for a-, b-and c-axis respectively. It has been found that uniaxial pressure applied along the c-axis strengthens the second order phase transition but applied along the directions perpendicular to the c-axis it may induce a tricritical point. The critical uniaxial pressure was estimated from the ratio C + /C − against X to be about 2.4 kbar. A tentative description of the mechanism of changes in the phase transition order is given. The phenomenological relation describing γ i is also discussed.

Effect of Uniaxial Pressure on the Ferroelectric Phase Transition in Pb5Ge3O11:Ba Crystals

“…LGO:Ba 366 750 1.70 ± 0.05 2.13 1.75 ± 0.05 −(7 ± 1) − (11 ± 2) paraelectric-ferroelectric PT is of second order for the crystal studied in agreement with earlier findings [6,13]. Now, we turn to discuss the results obtained for Pb 4.75 Ba 0.25 Ge 3 O 11 crystal.…”

“…The transition temperature T c , determined as the temperature at which the electric permittivity reaches its maximum, depends weakly on the measuring frequency and increases by only 0.5 K in the applied frequency range 100 Hz to 100 kHz. Dispersion of ε max was observed both in the ferroelectric and paraelectric phases [13,15]. The values of ε c obtained both at room temperature or near the phase transition temperature for the two crystals studied change slightly depending on previous thermal and mechanical treatment of the chosen samples.…”

“…In the case of pure LGO crystal the reciprocal of the electric permittivity ε c obeys the Curie-Weiss law [6,13]. The Curie-Weiss temperature T 0 is about 2.5 • C lower than T c ≈ 450 K for these crystals.…”

“…Temperature was varied within the range 300 to 500 K, at a rate 1 K/min in subsequent cycles of heating and cooling. Other details of experiment were the same as described previously [13].…”

“…Recent studies of the effect of uniaxial pressure on the ferroelectric phase transition of LGO single crystal suggests that it could be possible to induce the tricritical point by this approach [13]. Moiseenko et al [14] reported a jump-like change in the hyper-Rayleigh light scattering at T c = 438 K in the LGO crystals slightly doped with lanthanum.…”