Abstract
Relaxor ferroelectrics show substantial responses to electric fields. The key difference from normal ferroelectrics is a temperature-dependent inhomogeneous structure and its dynamics. The lead-based complex perovskite Pb(In1/2Nb1/2)O3 is an intriguing system in which the inhomogeneous structure can be controlled by thermal treatment. Herein, we report investigations of the phase transitions in single crystals of Pb(In1/2Nb1/2)O3 via changing the degree of randomness in which In and Nb occupy the B site of the ABO3 perovskite structure. We studied the dynamic properties of the structure using inelastic light scattering and the static properties using diffuse X-ray scattering. These properties depend on the degree of randomness with which the B site is occupied. When the distribution of occupied In/Nb sites is regular, the antiferroelectric phase is stabilised by a change in the collective transverse-acoustic wave, which suppresses long-range ferroelectric order and the growth of the inhomogeneous structure. However, when the B site is occupied randomly, a fractal structure grows as the temperature decreases below T*~475 K, and nanosized ferroelectric domains are produced by the percolation of self-similar and static polar nanoregions.
Highlights
Relaxors are a special class of inhomogeneous systems in which mesoscopic polar regions induce giant dielectric and electromechanical responses[3,4,5]
In PIN, the arrangement of In and Nb can be controlled thermally, and the resulting structures are broadly classified into two categories: (1) a disordered PIN (D-PIN) in which In and Nb ions randomly occupy B sites in equal site numbers and (2) an ordered PIN (O-PIN) in which In and Nb ions are 1:1 ordered[23,24,25]
D-PIN exhibits relaxor behaviour with a freezing temperature at Tf ~ 240 K, whereas O-PIN exhibits a first-order antiferroelectric phase transition at TN ~ 430 K
Summary
Relaxors are a special class of inhomogeneous systems in which mesoscopic polar regions induce giant dielectric and electromechanical responses[3,4,5]. We can understand relaxors in the same conceptual framework as BaTiO3, using the Comes–Guinnier–Lambert model in which the dynamic PNRs in relaxors correspond to nanometre-sized regions with time-dependent polarization[7,8,9,10]. We converted this image to a 2-bit image (Ising system), as shown, and we applied three successive 3 × 3 block-spin renormalisations [Fig. 1(c)–(e)]. By comparing D-PIN with O-PIN, we can discuss the crossover from a normal phase transition to relaxor freezing behaviour and clarify the connection between random electric fields and the origin of relaxors with wide distributions of static and dynamic fluctuations
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