High pressure synthesis of BiCrO3, a candidate for multiferroism

Review on Synthesis and Properties of Lithium Lanthanum Titanate

The rapid development of portable electronic devices and the efforts to find alternatives to fossil fuels have triggered the rapid development of battery technology. The conventional lithium-ion batteries have reached a high degree of sophistication. However, improvements related to specific capacity, charge rate, safety and sustainability are still required. Solid state batteries try to answer these demands by replacing the organic electrolyte of the standard battery with a solid (crystalline, but also polymer and hybrid) electrolyte. One of the most promising solid electrolytes is Li3xLa2/3-xTiO3 (LLTO). The material nevertheless presents a set of key challenges that must be resolved before it can be used for commercial applications. This review discusses the synthesis methods, the crystallographic and the ionic conduction properties of LLTO and the main limitations encountered through a number of selected studies on this material.

Solid Solutions between BiMnO3 and BiCrO3

Solid solutions BiMn_1-xCr_xO₃ (0 ≤ x ≤ 1) have been prepared at 6 GPa and 1370-1620 K. Their structural properties have been studied with synchrotron X-ray powder diffraction, and their physical properties have been investigated by dc/ac magnetic, specific heat, dielectric, and differential scanning calorimetry measurements. A magnetic phase diagram of BiMn_1-xCr_xO₃ is established. A phase with orbital ordering observed in BiMnO₃ is suppressed at x > 0.1, accompanied by a drop in the ferromagnetic Curie temperature T_C from 101 K for x = 0 to 76 K for x = 0.15 and sharp changes in the lattice parameters. The T_C value monotonically decreases up to x = 0.3 (with T_C = 53 K). For intermediate compositions with x = 0.4, 0.5, spin-glass magnetic properties are found at 28 and 24 K, respectively. The Néel temperature T_N linearly increases from 36 K for x = 0.6 to 111 K for x = 1.0. A spin-reorientation transition is observed at 61 K for x = 0.9 and 72 K for x = 1.0. Re-entrant spin-glass transitions are also observed for samples with x = 0.3, 0.6, 0.7 by ac susceptibility at low temperatures. At high temperatures, a structural phase transition from C2/c to Pnma symmetry is observed for all compositions with a monotonic change of the phase transition temperature. The magnetic phase diagram from the BiMnO₃-rich side (x ≤ 0.5) resembles a phase diagram of BiMn_1-xSc_xO₃ solid solutions, indicating that the nature of substituting cations (magnetic or nonmagnetic) is not crucial for doped BiMnO₃.

Magnetic properties of solid solutions between BiCrO3 and BiGaO3 with perovskite structures

Magnetic properties of BiCr1-x Ga x O3 perovskite-type solid solutions are reported, and a magnetic phase diagram is established. As-synthesized BiCrO3 and BiCr0.9Ga0.1O3 crystallize in a monoclinic (m) C2/c structure. The Néel temperature (TN) decreases from 111 K in BiCrO3 to 98 K in BiCr0.9Ga0.1O3, and spin-reorientation transition temperature increases from 72 K in BiCrO3 to 83 K in BiCr0.9Ga0.1O3. o-BiCr0.9Ga0.1O3 with a PbZrO3-type orthorhombic structure is obtained by heating m-BiCr0.9Ga0.1O3 up to 573 K in air; it shows similar magnetic properties with those of m-BiCr0.9Ga0.1O3. TN of BiCr0.8Ga0.2O3 is 81 K, and TN of BiCr0.7Ga0.3O3 is 63 K. Samples with x = 0.4, 0.5, 0.6 and 0.7 crystallize in a polar R3c structure. Long-range antiferromagnetic order with weak ferromagnetism is observed below TN = 56 K in BiCr0.6Ga0.4O3, TN = 36 K in BiCr0.5Ga0.5O3 and TN = 18 K in BiCr0.4Ga0.6O3. BiCr0.3Ga0.7O3 shows a paramagnetic behaviour because the Cr concentration is below the percolation threshold of 31%.

Identifying the 'inorganic gene' for high-temperature piezoelectric perovskites through statistical learning

This paper develops a statistical learning approach to identify potentially new high-temperature ferroelectric piezoelectric perovskite compounds. Unlike most computational studies on crystal chemistry, where the starting point is some form of electronic structure calculation, we use a data-driven approach to initiate our search. This is accomplished by identifying patterns of behaviour between discrete scalar descriptors associated with crystal and electronic structure and the reported Curie temperature (T_C) of known compounds; extracting design rules that govern critical structure–property relationships; and discovering in a quantitative fashion the exact role of these materials descriptors. Our approach applies linear manifold methods for data dimensionality reduction to discover the dominant descriptors governing structure–property correlations (the ‘genes’) and Shannon entropy metrics coupled to recursive partitioning methods to quantitatively assess the specific combination of descriptors that govern the link between crystal chemistry and T_C (their ‘sequencing’). We use this information to develop predictive models that can suggest new structure/chemistries and/or properties. In this manner, BiTmO₃–PbTiO₃ and BiLuO₃–PbTiO₃ are predicted to have a T_C of 730^°C and 705^°C, respectively. A quantitative structure–property relationship model similar to those used in biology and drug discovery not only predicts our new chemistries but also validates published reports.

Dielectric, structural and Raman studies on (Na(0.5)Bi(0.5)TiO(3))((1 - x))(BiCrO(3))(x) ceramic

Dielectric, structural and Raman investigations were carried out on a perovskite-based solid solution of (NBT)((1 - x))(BiCrO(3))(x) (x = 0.00, 0.05, 0.10 and 0.15). The crystal structure is rhombohedral, R3c, for these compositions and the anti-phase (a( - ) a( - ) a( - )) tilt angle decreases with increasing BiCrO(3) content. The temperature and frequency dependent dielectric measurements show that the phase transition temperatures T(d) and T(R - T) decrease, while T(m) increases, almost linearly with an increase in BiCrO(3) content. An anomalous increase in the relative dielectric permittivity is observed at higher temperature (T > T(d)) and higher BiCrO(3) content. However, at lower temperature (T < T(d)) the dielectric permittivity decreases with an increase in BiCrO(3) content. These effects are explained on the basis of the dynamics of oxygen defects produced due to charge compensation. The defect related bands are observed in the Raman spectra of (NBT)((1 - x))(BiCrO(3))(x).