Frequency-independent dielectric losses (1/fnoise) in PLZT relaxors at low temperatures

Abstract

Dielectric properties of the relaxor ferroelectric ceramics PLZT 8/65/35 and 9.5/65/35 were studied in the broad frequency range of 100 Hz-1 THz at low temperatures below the freezing temperature. Nearly frequency-independent dielectric losses were observed up to 1 GHz on cooling down to 10 K. Their magnitude decreases exponentially with temperature, but remains remarkable high down to 10 K. A Landau-type thermodynamic model based on the perovskite structure near the morphotropic phase boundary is proposed for calculating the energy barriers for polarization reversal near the polar cluster boundaries and explaining the broad distribution function of relaxation times, which fits the observed frequency dependences of permittivity and losses below 1 GHz. High dielectric losses in the submillimetre region were explained by shear wave emission of vibrating polar cluster walls in an ac electric field and by piezoelectric resonances on polar clusters.

Infrared, terahertz, and microwave spectroscopy of the soft and central modes in Pb(Mg1/3Nb2/Nuzhnyy1, Petzelt2, Bovtun3 et al. 2017Phys. Rev. B21160View full textAdd to dashboardCite

“…15 we plotted our '(ω) spectra for selected temperatures and it is seen that our exponent  evaluated from the range of ~10 6 -10 11 Hz decreases from ~1.6 at 500 K to ~1 below T f . The value  = 1 (see all our data above the MHz range at 100 K) corresponds to frequency-independent loss "(ω) generally appearing in relaxors below T f (also known as the 1/f noise) [38], see Fig. 12(a).…”

“…On the other hand, concerning the relaxational dispersion of PNDs in relaxor perovskites, a mesoscopic theory based on the Landau approach close to the morphotropic phase boundary was suggested in Ref. [38], which explains well particularly the low-temperature response (T < T f ) of frequency-independent losses (within the limits of accessible frequency range) and their temperature dependence. The theory [38] is based on the assumption that the total dielectric response is due to a composite of frozen PNDs, which do not contribute to the relaxational response, and of dynamic dipoles at the PND boundaries, which can still flip between their possible orientations over some temperature independent statistical distribution of potential energy barriers.…”

What Can Be Expected From Lead-Free Piezoelectric Materials?

“…This may not be the case in unpoled BNT-BT which exhibits pseudocubic structure in compositions close to MPB 55,56 and probably not well-developed domain structure. Alternatively, the "microwave" dispersion may be related to vibration of polar cluster boundaries, as reported for (Pb,La)(Zr,Ti)O 3 by Rychetsky et al 74 On the other hand, the slow "logarithmic" dispersion is stronger in BNT-BT than in soft PZT. One reason for this may be a high disorder of BNT-BT and contribution to the dielectric dispersion of polarization reversal near polar cluster boundaries.…”

“…One reason for this may be a high disorder of BNT-BT and contribution to the dielectric dispersion of polarization reversal near polar cluster boundaries. 74 Another is that the temperature of the transition into the nonpolar phase is closer to room temperature in BNT-BT (100-180 • C) than in PZT (>350 • C) and the mobility of domain walls/polar cluster boundaries may be higher in BNT-BT. Again, taking the value of the permittivity at 100 kHz as the reference, one can infer from Fig.…”

Compositional disorder, polar nanoregions and dipole dynamics in Pb(Mg1/3Nb2/3)O3-based relaxor ferroelectrics

“…The other contributions related to soft phonons, motion of the boundaries of (static and dynamic) PNR, etc. also exist [9,27,28]. In particular, different polar-phonon modes related to CORs and compositionally disordered regions were revealed in the IR reflectivity spectra of 0.65 Pb(Mg 1/3 Nb 2/3 )O 3 --0.35 PbTiO 3 ceramics [29].…”