Abstract
Outstanding electrical properties of solids are often due to the composition heterogeneity and/or the competition between two or more sublattices. This is true for superionic and superprotonic conductors and supraconductors, as well as for many ferroelectric materials. As in PLZT ferroelectric materials, the exceptional ferro- and piezoelectric properties of the PMN-PT ((1−x)PbMg1/3Nb2/3O3−xPbTiO3) solid solutions arise from the coexistence of different symmetries with long and short scales in the morphotropic phase boundary (MPB) region. This complex physical behavior requires the use of experimental techniques able to probe the local structure at the nanoregion scale. Since both Raman signature and thermal expansion behavior depend on the chemical bond anharmonicity, these techniques are very efficient to detect and then to analyze the subtitle structural modifications with an efficiency comparable to neutron scattering. Using the example of poled (field cooling or room temperature) and unpoled PMN-PT single crystal and textured ceramic, we show how the competition between the different sublattices with competing degrees of freedom, namely the Pb-Pb dominated by the Coulombian interactions and those built of covalent bonded entities (NbO6 and TiO6), determine the short range arrangement and the outstanding ferro- and piezoelectric properties.
Highlights
Heterogeneity and electrical properties: solid solution a wrong conceptMost of the outstanding electrical/electrochemical/magnetic properties result from a competition between different potentials of the chemical bonding and structure
The temperature of the maximum values are different, namely 120 °C and 140 °C, and the curves have a rather relaxor character [45,46,47]. This suggests that the ferroelectric state can be achieved after the FC
Similar behavior is observed for RT poled highly textured ceramic: two transitions near 70 and 160 °C, already detected by dielectric measurements, are well seen, whereas the thermal expansion curve reveals the presence of another weak transformation in the vicinity of 200 °C
Summary
Most of the outstanding electrical/electrochemical/magnetic properties result from a competition between different potentials of the chemical bonding and structure. In a crystal, as a function of the crystalline axis, different types of bonds can simultaneously be present. This discovery was first made for KNiF4 by J.B. Goodenough and is the origin of supraconductivity [4,5,6,7]. At the limit between these two phases, the atoms undergo a chemical field and bonding that are different from those present in the phase core. The limit between two symmetries will depends on the observation scale
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