Size and Strain Effects on Relaxor Ferroelectric Properties of PbSc_(0.5)Nb_[(1-x)/2]Ta_(x/2)O_3 Thin Films and Nanoceramics

摘要

PbSc_(0.5)Nb_[(1-x)/2]Ta_(x/2)O_3 (PSNT for x = 0.3, PST for x = 1) nanoceramics and thin films were prepared by high energy ball mill with solid state reaction technique and pulse laser deposition (PLD) respectively. A comparative study of the microstructure, dielectric properties, and polarization of PSNT and PST thin films and nano ceramics were carried out over a wide range of temperature (100 K-600 K) and frequency (100 Hz to 1 MHz). High Resolution Transmission Electron Microscopy (HRTEM) image of PSNT and PST thin films indicate the presence of small polar nano regions (PNRs) and long range ordered regions in crystal lattice plane respectively. PST nanoceramics (PST-N) showed normal ferroelectric behavior where as its thin film form (PST-F) illustrated relaxor behavior. PSNT nanoceramics (PSNT-N) and its films (PSNT-F) demonstrated weak frequency dispersion and strong frequency dispersion in dielectric spectra respectively. A shift in dielectric maximum temperature (T_m) towards lower temperature side i.e. 65 K and 85 K were observed for PSNT-F and PST-F compared to their nanoceramices indicates greater role of substrate-electrode-interface strain on dielectric properties. Well behaved hysteresis at room temperature for PSNT-F point toward strong competition between short range order and long range order. A weak slim hesteresis for PST-F were observed at room temperature suggesting the existence of polar nano regions far above dielectric maximum temperature.