High‐pressure Raman spectroscopy of nano‐structured ABO₃ perovskites: a case study of relaxor ferroelectrics

Abstract

A large number of outstanding physical properties observed in perovskite-type oxides, such as giant piezoelectricity, colossal magneto-resistance and high-T c superconductivity, are related to an intrinsic nano-scaled local structure. For instance, the presence of a nano-scaled structure is characteristic of so-called relaxor ferroelectrics (relaxors), which have attracted considerable attention since the recent discovery of ultra-high strain and giant piezoelectric properties. In this paper we review, through a case study of relaxors, how the combination of the external parameter high-pressure and Raman spectroscopy allows an instructive investigation of nano-scaled perovskites, which is often at best a difficult task for conventional 'average-structure' techniques such as diffraction. We show that perovskite-type relaxors present important pressure instabilities with respect to both cation sizes and we suggest that the latter instabilities might well be at the origin of the reduced dielectric performances that are observed for strained thin-film relaxors. Finally, we briefly illustrate how the approach might be used for nano-scaled manganite-type oxides.

Probing the Nanodomain Origin and Phase Transition Mechanisms in (Un)Poled PMN-PT Single Crystals and Textured Ceramics

“…The Raman spectra of both poled and unpoled PMN-29%PT single crystal and PMN-34.5%PT highly textured ceramic look at a first view very similar to those usually observed for relaxor ferroelectric samples [54,60,61,62,63,70,73,74,94,95,96]. They consist of a number of broad bands observed over the whole measured temperature range.…”

“…Note that the high structural disorder is directly responsible for very broad bands [14,28]. The eventual presence of the polar nanoregions (PNR) with the distinct local symmetry different than this cubic one, due to the ions being displaced from their high mean symmetry positions, give rise to the local electric dipoles [60,61,62,63,70,73,74,94,95,96] and the local distortions from cubic symmetry allow the Raman activity. The presence of chemically ordered clusters additionally complicates understanding of the Raman spectrum.…”

Transformation processes in relaxor ferroelectric PbSc0.5Ta0.5O3heavily doped with Nb and Sn

“…Exceptionally high piezoelectric and electro-optic responses have been detected in solid solutions of Pb-based relaxors (Pb occupying the A-position of the perovskite-type structure) and PbTiO 3 [2], whose local structure closely resembles the nanoscale atomic arrangements of relaxors [3]. To better understand the intrinsic structural features of relaxors and hence the structureproperty relationships, temperature-as well as pressureinduced structural transformations have been extensively studied by X-ray and neutron diffraction [4][5][6][7][8][9], pair-distribution-function analysis [10,11], quasielastic [12] and inelastic neutron scattering [13], Raman and infrared (IR) spectroscopy [14][15][16][17], Brillouin spectroscopy [18], nuclear magnetic resonance [19], X-ray absorption spectroscopy [20,21], piezoresponse force microscopy [22,23], acoustic emission [24] and dielectric measurements [25][26][27][28]. It is currently accepted that the broad frequency-dispersive peak of the dielectric permittivity as a function of temperature, which is a unique property of relaxors, is due to the existence of dynamic polar nanoregions (PNRs) flipping between different orientation states, each of which corresponds to one of the possible crystallographic directions along which the cubic unit cell can be distorted corresponding to a polar class.…”

Structural and electrical properties of bismuth magnesium titanate substituted lead-free sodium bismuth titanate ceramics

“…9E modes are both Raman and IR active and 5B 1 modes are silent. From [29][30][31]. On substitution of BMT in NBT an increase in frequency of the two modes namely 247 and 281 cm -1 related to TiO 6 octahedra vibration modes are noticed which may be due to the rotational change of the oxygen octahedra.…”