Possible nature of a new quantum paraelectric state in incipient ferroelectrics and its role in spectroscopic effects

Abstract

A mechanism of a new quantum paraelectric state (QPS) formation in incipient ferroelectrics of SrTiO₃-type and its role in spectroscopic effects are considered. The proposed model is based on the assumption that the tunnelling off-center ions appear in the host lattice in the vicinity of strong elastic defects. The corresponding order-disorder type clusters are responsible for QPS. The local transition in such clusters leads to ferroelectric microdomain formation. The corresponding new modes have an order-disorder nature (cooperative tunnelling modes) as well as displace one (a new acoustic-like microdomain mode). But in both cases the mixing of different type of modes plays an important role. This model gives the possibility to explain the main experimental results.

Key Words:

• Incipient ferroelectric
• perovskite
• tunnelling
• elastic defects
• off-center ions
• quantum paraelectric state