Strain-Induced Relaxor Behavior in PbSc0.50Nb0.25Ta0.25O3 Thin Films: A Comparison with Nanoceramics
Comparative studies of the microstructure, micro-Raman spectroscopy, and dielectric properties of PbSc0.50Nb0.25Ta0.25O3 (PSNT) thin films and nanoceramics were carried out over a wide range of temperature (100–520 K) and frequency (100 Hz to 1 MHz). The microstructure of PSNT films revealed an in-plane compressive strain, whereas PSNT nanoceramics showed an average grain size of 10–15 nm although these nanoordered regions are not capable of producing relaxor behavior. We have observed a shift of 65 K in the dielectric maxima temperature in PSNT films toward the lower temperature side compared with bulk, which confirms the in-plane compressive strain in the films. We have proposed a dielectric model to calculate the shift in dielectric maxima temperature. Using our experimental data of PSNT thin films, the theoretical model predicted a shift of 62 K in the dielectric maxima temperature, which matched well with our experimental observation. The modified Curie–Wiess law showed a broad relaxation (∼2) and a higher disorder level (=90 K) for PSNT thin films compared with PSNT nanoceramics having ∼1.60 and =15 K. Well-behaved hysteresis loops were observed in a broad temperature range for PSNT thin films and slim hysteresis for nanoceramics, indicating a relaxor ferroelectric and diffused ferroelectric phase transition (DFPT) nature, respectively. The temperature-dependent micro-Raman spectroscopy revealed that the ferroelectric state in PSNT nanoceramics was accompanied by the appearance of a new peak as a shoulder at ∼80 cm−1 to the lowest F2g mode ∼57 cm−1. Its half-widths and intensity reduced to zero near the phase transition temperature, whereas the A1g mode showed a doublet namely at (805 and 830 cm−1) below DFPT and an intermediate singlet frequency at 820 cm−1 above DFPT. The micro-Raman spectra for the thin film matched quite well with the nanoceramics, except that the missing second F2g mode at ∼360 cm−1 was interpreted due to a shorter coherence length in the dipole arrangement in thin films. The in-plane compressive strain, dipole arrangement, and the size of the nanoordered regions vary the dielectric response of the PSNT films compared with the nanoceramics.
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Document Type: Research Article
Affiliations: Department of Physics, and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan 00931-3343, Puerto Rico
Publication date: 01 June 2008