Ferroelectrics carry a switchable spontaneous electric polarization. This polarization is usually coupled to strain, making ferroelectrics good piezoelectrics. When magnetism, they become so-called multiferroic systems, field that has been widely investigated since 2003. While are birefringent and non-linear optically transparent materials, the coupling of with optical properties received, 2009, renewed attention, triggered notably by low-bandgap suitable for sunlight spectrum absorption...

This review stands in the larger framework of functional materials by focussing on heterostructures rare-earth nickelates, described chemical formula RNiO3 where R is a trivalent = La, Pr, Nd, Sm, ..., Lu. Nickelates are characterized rich phase diagram structural and physical properties serve as benchmark for physics transitions correlated oxides electron–lattice coupling plays key role. Much recent interest nickelates concerns heterostructures, that single layers thin film, multilayers or...

The entire zone-center phonon spectrum of the $R3c$ ferroelectric antiferromagnetic phase bismuth ferrite is computed using a first-principles approach based on density functional theory. Two modes exhibiting eigendisplacement vectors that strongly overlap with atomic distortions taking place at structural transition are identified and give support to displacive character. Both Raman infrared reflectivity spectra also computed, providing benchmark theoretical results for assignment...

We report a temperature-dependent Raman scattering investigation of the multiferroic material bismuth ferrite ${\mathrm{BiFeO}}_{3}$ (BFO). The observed loss spectrum at ferroelectric Curie temperature ${T}_{C}$ should be in agreement with cubic $Pm\overline{3}m$ structure high-temperature paraelectric phase. Surprisingly, ferroelectric-to-paraelectric phase transition is not soft-mode driven, indicating nonconventional ferroelectric. Furthermore, our results reveal pronounced phonon...

We report a Raman scattering study of six rare earth orthoferrites RFeO3, with R = La, Sm, Eu, Gd, Tb, Dy. The use extensive polarized SmFeO3 and first-principles calculations enable the assignment observed phonon modes to vibrational symmetries atomic displacements. spectra their comparison throughout whole series allows correlating orthorhombic structural distortions RFeO3 perovskites. In particular, positions two specific Ag scale linearly FeO6 octahedra tilt angles, allowing distortion...

Recently, piezoelectric-based catalysis has been demonstrated to be an efficient means and promising alternative sunlight-driven photocatalysis, where mechanical vibrations trigger redox reactions. Here, 60 nm-size BiFeO3 nanoparticles are shown very effective for piezo-degrading Rhodamine B (RhB) model dye with record degradation rate reaching 13 810 L mol-1 min-1 , even 41 750 (i.e., 100% RhB within 5 min) when piezocatalysis is synergistically combined sunlight photocatalysis. These...

The (Na1 - x Kx )0.5 Bi0.5 TiO3perovskite solid solution is investigated using x-ray diffraction (XRD) and Raman spectroscopy in order to follow the structural evolution between end members Na0.5 TiO3(rhombohedral at 300 K) K0.5 TiO3(tetragonal K). spectra are analysed with special regard hard modes suggest existence of nano-sized Bi3+ TiO3and 2x K2x )+TiO3clusters. complementary use XRD suggests, contrast previous reported results, that rhombohedral tetragonal phase transition goes through...

We report high-pressure Raman measurements (up to 19 GPa) on the perovskite-type relaxor ferroelectric sodium-bismuth-titanate, ${\mathrm{Na}}_{0.5}{\mathrm{Bi}}_{0.5}{\mathrm{TiO}}_{3}$ (NBT). Distinct changes in spectra have been analyzed light of a rhombohedral-to-orthorhombic $(R3c\ensuremath{-}\mathrm{t}\mathrm{o}\ensuremath{-}\mathit{Pnma})$ phase transition. Results show that this transition, involving change tilt system and cation displacement, does not occur single step, but goes...

$\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ ceramics were investigated by means of infrared reflectivity and time domain terahertz transmission spectroscopy at temperatures $20--950\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the magnetodielectric effect was studied $10--300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ with magnetic field up to $9\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. Below $175\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, sum polar phonon contributions permittivity corresponds value measured...

Regularly twinned domain structures are observed by scanning piezoforce microscopy on single crystalline grains of BiFeO3 ceramics being grown a special low temperature sintering process. The domains considerably larger than those in thin films. Their spontaneous polarization comes close to that predicted theoretically and overcomes restrictions hitherto set bulk crystals. ferroelastic twin structure resembles classic T rhombohedrally distorted NiO, but is additionally superimposed...

We report a systematic investigation of orthorhombic perovskite-type RCrO3 powder samples by Raman scattering for nine different rare earth R3+ cations (R = Y, La, Pr, Sm, Gd, Dy, Ho, Yb, Lu). The room-temperature spectra and the associated phonon mode assignment provide reference data structural whole series orthochromites ab-initio calculations. chromite comparison with on other perovskites allows correlating modes distortions in series. In particular, two Ag are identified as octahedra...

A previous study of the growth conditions has shown that single-phase BiFeO3 thin films can only be obtained in a narrow pressure–temperature window and these display weak magnetic moment. Here, we more detail structure magnetism by means reciprocal space mapping, Raman spectroscopy neutron diffraction. X-ray data suggest is tetragonal for 70 nm thick changes to monoclinic 240 films, thus remaining different from bulk (rhombohedral) structure. In monoclinically distorted film, diffraction...

Abstract AB O 3 perovskite‐type solid solutions display a large variety of structural and physical properties, which can be tuned by chemical composition or external parameters such as temperature, pressure, strain, electric, magnetic fields. Some show remarkably enhanced properties including colossal magnetoresistance giant piezoelectricity. It has been recognized that distortions, competing on the local level, are key to understanding tuning these remarkable yet, it remains challenge...

We report a temperature-dependent investigation of the multiferroic perovskite bismuth ferrite ${\text{BiFeO}}_{3}$ (BFO) by using x-ray powder diffraction together with differential scanning calorimetry measurements. Our results provide evidence that paraelectric phase above ${T}_{c}=820\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ is not cubic but distorted and can be well refined in monoclinic $P{2}_{1}/m$ space group. An equivalent structure reconstructed based on $C2/m$ group...

We report experimental evidence for pressure instabilities in the model multiferroic ${\text{BiFeO}}_{3}$ and, namely, reveal two structural phase transitions around 3.5 and 10 GPa by using diffraction far-infrared spectroscopy at a synchrotron source. The intermediate crystallizes monoclinic space group, with octahedra tilts small cation displacements. When is increased further displacements (and thus polar character) of suppressed above GPa. nonpolar orthorhombic $Pnma$ structure observed...

Correlation between spin-phonon coupling and the magnetoelectric properties of ${\text{EuMnO}}_{3}$ ${\text{GdMnO}}_{3}$ were investigated using ceramic samples in this work. The experimental results evidence a stronger than ${\text{EuMnO}}_{3}$, as well clear anomaly phonon contribution for dielectric constant. This is located at paramagnetic-incommensurate antiferromagnetic phase-transition temperature ${\text{GdMnO}}_{3}$, corroborating existence effect system. absence due to existing...

We investigate the cubic to tetragonal phase transition in pressure-temperature diagram of strontium titanate SrTiO3 (STO) by means Raman spectroscopy and X-ray diffraction on single crystal samples. experiments are performed at room temperature, 381 467 K up 53 GPa, 30 GPa 26 respectively. The observation superstructure reflections patterns provides evidence that undergoes all investigated temperatures a pressure-induced from I4/mcm phase, identical low-temperature phase. No other is...

We investigate the high-pressure phase transitions in BiFeO${}_{3}$ by single-crystal and powder x-ray diffraction, as well Raman spectroscopy. Six are reported 0--60-GPa range. At low pressures, four evidenced at 4, 5, 7, 11 GPa. In this range, crystals display large unit cells complex domain structures, which suggests a competition between tilt systems possibly off-center cation displacements. The nonpolar $Pnma$ remains stable over pressure range 38 GPa, where distortion (tilt angle)...

A marked conductivity enhancement is reported in 6–11 unit cell LaNiO 3 thin films. maximal also observed ab initio calculations for films of the same thickness. In agreement with results from state art scanning transmission electron microscopy, reveal a differentiated film structure comprising characteristic surface, interior, and heterointerface structures. Based on this observation, three‐element parallel conductor model considered leads to conclusion that cells, stems onset...

Abstract Memristive devices based on mixed ionic–electronic resistive switches have an enormous potential to replace today's transistor‐based memories and Von Neumann computing architectures thanks their ability for nonvolatile information storage neuromorphic computing. It still remains unclear however how ionic carriers are propagated in amorphous oxide films at high local electric fields. By using memristive model LaFeO 3 with either or epitaxial nanostructures, we engineer the structural...

Bulk photovoltaic current in ferroelectric lithium niobate increases by 75% under a compressive mechanical stress of only 10 MPa.

Abstract Many material properties such as superconductivity, magnetoresistance or magnetoelectricity emerge from the non-linear interactions of spins and lattice/phonons. Hence, an in-depth understanding spin–phonon coupling is at heart these properties. While most examples deal with one magnetic lattice only, simultaneous presence multiple orderings yield potentially unknown We demonstrate a strong in SmFeO 3 that emerges interaction both, iron samarium spins. probe this remarkably large...

We report high-pressure Raman measurements (up to 27 GPa) on the perovskite-type relaxor ferroelectric ${\mathrm{BaTi}}_{0.65}{\mathrm{Zr}}_{0.35}{\mathrm{O}}_{3}({\mathrm{BTZ}}_{35}).$ Distinct changes of spectra with increasing pressure illustrate that ${\mathrm{BTZ}}_{35}$ presents important instabilities leading at least two phase transitions around 5.7 GPa and 15.1 GPa, respectively. The observed pressure-induced spectral for are reminiscent features have been pure...

Extended x-ray absorption fine structure experiments at the Zr $K$ edge were carried out on perovskite relaxor ferroelectrics $\mathrm{Ba}{\mathrm{Ti}}_{1\ensuremath{-}x}{\mathrm{Zr}}_{x}{\mathrm{O}}_{3}$ (BTZ) $(x=0.25,0.30,0.35)$, and $\mathrm{Ba}\mathrm{Zr}{\mathrm{O}}_{3}$ for comparison. Structural information up to $4.5\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ around atoms is obtained, revealing that local differs notably from average $Pm\overline{3}m$ cubic deduced diffraction. In...