SIZE AND STRAIN EFFECTS ON RELAXOR FERROELECTRIC PROPERTIES OF PBSC_0.5NB_{(1 −x)/2}TA_x/2O₃ THIN FILMS AND NANOCERAMICS

ABSTRACT

PbSc_0.5Nb_{(1 −x)/2}Ta_x/2O₃(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 compare 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.

Keywords:

• Relaxor ferroelectric
• thin films
• strain
• HRTEM

ACKNOWLEDGMENTS

This work was partially supported by DOD W911NF-06-1-0030. The authors thank the Cornell Center for Material Research (CCMR) for the HRTEM measurements at Advanced Microscopy Facilities. M. Correa acknowledgement the IFN fellowship that sponsored the HRTEM studies at CCMR.