Pressure as a probe of the physics of 18O - substituted SrTiO3.
- Tokyo Institute of Technology, Yokohama, Japan
Studies of the dielectric properties and phase behavior of an {sup 18}O-substituted SrTiO{sub 3} (>97% {sup 18}O), or STO-18, crystal at 1 bar and as functions of hydrostatic pressure and applied dc biasing electric field have shed much light on the mechanism of the {sup 18}O-induced ferroelectric transition in this material. Dielectric measurements reveal an equilibrium phase transition (T{sub c} {approx_equal} 24K at 1 bar) and an enhancement of the static dielectric constant {var_epsilon} over that of normal (i.e., {sup 16}O) SrTiO{sub 3}, or STO-16, over a large temperature range above T{sub c}. This enhancement is quantitatively shown to be attributed to additional softening of the ferroelectric soft-mode frequency ({omega}{sub s}) of STO-16, in agreement with lattice dynamic calculations. Thus, in STO-18, two effects due to the heavier mass of {sup 18}O conspire to induce the transition: (i) this additional softening of {omega}{sub s} and (ii) damping of quantum fluctuations. Pressure lowers T{sub c} at the large initial rate of 20 K/kbar and completely suppresses the ferroelectric state leading to a quantum paraelectric state at 0.7 kbar, confirming earlier results. Very large effects of a biasing dc electric fields on the peak temperature and {var_epsilon} are also observed in the quantum regime reflecting the small characteristic energies of the system. The results also reveal a dielectric relaxation process near 10 K with interesting properties. The implications of all the results on our understanding of the physics of STO-18 are discussed.
- Research Organization:
- Sandia National Laboratories
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 1003917
- Report Number(s):
- SAND2003-2835J
- Journal Information:
- Proposed for publication in Physical Review B., Journal Name: Proposed for publication in Physical Review B. Journal Issue: 18 Vol. 69; ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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