Abstract
We report on a thermal-expansion study of the ferroelectric phase transition in insulating () and its evolution upon increasing charge-carrier concentration up to . Although electric polarization is screened by mobile charge carriers, we find clear signatures of the ferroelectric phase transition in the thermal-expansion coefficient of the weakly doped metallic samples. Upon increasing , the transition temperature and the magnitude of the anomalies in rapidly decrease up to a threshold carrier density above which broadened anomalies remain present. There is no indication for a sign change of as is expected for a pressure-dependent quantum phase transition with as the control parameter. Thus, the ferroelectriclike transition is either continuously fading away or it transforms to another low-temperature phase above , but this change hardly affects the temperature-dependent data.
- Received 23 July 2019
- Revised 27 September 2019
DOI:https://doi.org/10.1103/PhysRevB.100.195121
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