Low temperature specific heats of some PLZT ceramics

Abstract

The zero-field and field-dependent (E ≈ 40 kV/cm) specific heats of PZT 65/35, PLZT 9/65/35, PLZT 11/65/35, and PLZT 8/40/60 were measured in a vacuum calorimeter in the range 2-25 K. The Debye temperatures range from 119 K (11/65/35) to 132 K (9/65/35), and low-lying modes describable by an Einstein term (vE ≈ 30 cm-1) dominate the specific heats of all the ceramics between §3-15 K. The specific heats of PLZT 11/65/35 and 8/40/60 are field dependent, and this field dependence arises from a change in the number of Einstein oscillators rather than a change in the frequency. The field-dependent oscillator in PLZT 8/40/60 at 32.5 cm-1 is believed due to a combination of the E(TO) soft phonon and zone-boundary TA phonons which are degenerate at these temperatures. This picture is consistent with powder Raman data. The field-independent oscillators in PZT 65/35 (32 cm-1) and PLZT 9/65/35 (30 cm-1) are believed due to zone-boundary TA phonons. A T3/2 domain-wall contribution is observed at the lowest temperatures in PLZT 11/65/35 (the measurements do not extend to low enough temperatures to resolve this contribution in the other ceramics).