Nanometre-scale optical property fluctuations in Cu2ZnSnS4 revealed by low temperature cathodoluminescence

in Solar Energy Materials and Solar Cells (2018), 174

Nanometre-scale optical property fluctuations in Cu2ZnSnS4 revealed by low temperature cathodoluminescence

in Solar Energy Materials and Solar Cells (2017), 174

Bismuth-based perovskites as multiferroics

in Comptes Rendus Physique (2015), 16(2), 182-192

This review devoted to multiferroic properties of bismuth-based perovskites is divided into two parts. The first one focuses on BiFeO3and summarizes the recent progress made in the studies of its ... [more ▼]

This review devoted to multiferroic properties of bismuth-based perovskites is divided into two parts. The first one focuses on BiFeO3and summarizes the recent progress made in the studies of its pressure–temperature phase diagram and magnetoelectric coupling phenomena. The second part discusses in a more general way the issue of polar—and multiferroic—phases in BiBO3perovskites and the competition between ferroelectricity and other structural instabilities, from an inventory of recently synthesized compounds. [less ▲]

Jahn-Teller, Polarity, and Insulator-to-Metal Transition in BiMnO3 at High Pressure

in Physical Review Letters (2014), 112

The interaction of coexisting structural instabilities in multiferroic materials gives rise to intriguing coupling phenomena and extraordinarily rich phase diagrams, both in bulk materials and strained ... [more ▼]

The interaction of coexisting structural instabilities in multiferroic materials gives rise to intriguing coupling phenomena and extraordinarily rich phase diagrams, both in bulk materials and strained thin films. Here we investigate the multiferroic BiMnO3 with its peculiar 6s2 electrons and four interacting mechanisms: electric polarity, octahedra tilts, magnetism, and cooperative Jahn-Teller distortion. We have probed structural transitions under high pressure by synchrotron x-ray diffraction and Raman spectroscopy up to 60 GPa. We show that BiMnO3 displays under pressure a rich sequence of five phases with a great variety of structures and properties, including a metallic phase above 53 GPa and, between 37 and 53 GPa, a strongly elongated monoclinic phase that allows ferroelectricity, which contradicts the traditional expectation that ferroelectricity vanishes under pressure. Between 7 and 37 GPa, the Pnma structure remains remarkably stable but shows a reduction of the Jahn-Teller distortion in a way that differs from the behavior observed in the archetypal orthorhombic Jahn-Teller distorted perovskite LaMnO3. [less ▲]

Structures and Magnetism of the Rare-Earth Orthochromite Perovskite Solid Solution LaxSm1−xCrO3

in Inorganic Chemistry (2013), 52

A new mixed rare-earth orthochromite series, LaxSm1−xCrO3, prepared through single-step hydrothermal synthesis is reported. Solid solutions (x = 0, 0.25, 0.5, 0.625, 0.75, 0.875, and 1.0) were prepared by ... [more ▼]

A new mixed rare-earth orthochromite series, LaxSm1−xCrO3, prepared through single-step hydrothermal synthesis is reported. Solid solutions (x = 0, 0.25, 0.5, 0.625, 0.75, 0.875, and 1.0) were prepared by the hydrothermal treatment of amorphous mixed-metal hydroxides at 370 °C for 48 h. Transmission electron microscopy (TEM) reveals the formation of highly crystalline particles with dendritic-like morphologies. Rietveld refinements against high-resolution powder X-ray diffraction (PXRD) data show that the distorted perovskite structures are described by the orthorhombic space group Pnma over the full composition range. Unit cell volumes and Cr−O−Cr bond angles decrease monotonically with increasing samarium content, consistent with the presence of the smaller lanthanide in the structure. Raman spectroscopy confirms the formation of solid solutions, the degree of their structural distortion. With the aid of shell-model calculations the complex mixing of Raman modes below 250 cm−1 is clarified. Magnetometry as a function of temperature reveals the onset of low-temperature antiferromagnetic ordering of Cr3+ spins with weak ferromagnetic component at Néel temperatures (TN) that scale linearly with unit cell volume and structural distortion. Coupling effects between Cr3+ and Sm3+ ions are examined with enhanced susceptibilities below TN due to polarization of Sm3+ moments. At low temperatures the Cr3+ sublattice is shown to undergo a second-order spin reorientation observed as a rapid decrease of susceptibility. [less ▲]