 |
 |
 |
|
|
|
|
Dr. Ang Chen's Lab
Quantum Paraelectric Behavior
SrTiO3 is a very special dielectric. Although, from 300K down to 50K, the temperature dependence of the permittivity of SrTiO3 follows the Curie-Weiss law, just as in ordinary ferroelectrics, with a Curie temperature Tc = 35.5K; no further permittivity peaks appear as the temperature decreases further, and the permittivity levels off at a high value at extremely low temperatures. The suppression of ferroelectricity is attributed to quantum fluctuations at low temperatures. Therefore it is named as a “quantum paraelectric” by K.A. Müller and H. Burkhard, see, Phys. Rev. B19, 3593 (1979).
Beside SrTiO3, KTaO3 is considered as another typical “quantum paraelectric”. Later, CaTiO3 is also thought as a “quantum paraelectric”. Recently, a series of solid solutions (Ln,Na)TiO3, Ln= La, Nd, .., are also attributed to “quantum paraelectrics”.
A very interesting characteristic for “quantum paraelectrics” is, because they are on the verge to ferroelectricity, when doped with moderate amounts of impurities, or in external electric fields, polar order is induced. However, in the literature, the low-temperature phases in the doped compounds have been interpreted rather controversially: as model systems of dipolar glasses, as long-range and as short-range ordered polar states.
Dr. Ang Chen and his colleagues have been studying the dielectric/ferroelectric/electrical -transport properties of quantum paraelectric and their derivatives, and trying to understand their physics since 1990’s. The following papers are our results in this area.
Other papers related this topic are also shown below.
ZHI Yu and CHEN Ang, Dielectric and Conduction Anomalies in La-doped SrTiO3 with Suppression of Quantum-Paraelectric, Applied Physics Letters, 80[4], 643-5 (2002).
ZHI Yu, CHEN Ang, and L. E. Cross, Oxygen-vacancy-related Dielectric anomalies in La:SrTiO3, Applied Physics Letters, 74[20], 3044-46(1999).
CHEN Ang, J. F. Scott, ZHI Yu, H. Ledbetter, and J.L. Baptista, Dielectric and Ultrasonic Anomalies at 22K, 37K and 65K in SrTiO3, Physical Review B59, 6661-64(1999).
CHEN Ang, ZHI Yu, J. Hemberger, P. Lunkhemer, and A. Loidl, Dielectric anomalies in bismuth doped SrTiO3; Defect modes at low impurity concentrations, Physical Review B59, 6665-69(1999).
CHEN Ang, ZHI Yu, P. Lunkhemer, J. Hemberger, and A. Loidl, Dielectric relaxation modes in bismuth doped SrTiO3; The Relaxor Behavior, Physical Review B59, 6670-74(1999).
CHEN Ang and ZHI Yu, Phonon-coupled impurity dielectric modes in Bi:SrTiO3, Physical Review B61, 11363-66(2000).
CHEN Ang, ZHI Yu, P. M. Vilarinho and J. L. Baptista, Bi:SrTiO3: A quantum ferroelectric and a relaxor, Physical Review B57, 7403-06(1998).