2009 年 19 巻 2 号 p. 95-100
Current topics of relaxor studies are summarized with focusing on the quantum relaxor KTaO3 doped with Li, which bears all the characteristics of the prototype relaxor; (1) dielectric response described by the Vogel-Fulcher law, (2) history dependence of the order parameter, (3) slow development of the order parameter after an extremely long incubation time, and (4) nucleation and growth of the polar nano-region in non-polar matrix. In addition, the tri-critical point that separates the first and second order phase transitions is located in the vicinity of the line of critical end points, which enhances the dielectric response of the system. This kind of critical behavior is originated from the complex competition between a long-range Coulomb interaction, a short-range dipolar interaction, a quantum fluctuation (zero-point vibration) and a random field. This phenomenon is promising for the future trend of functional material quests.
