High-Pressure Hydrothermal Crystal Growth and Multiferroic Properties of a Perovskite YMnO3

Colossal Linear Magnetoelectricity in Polar Magnet Fe_{2}Mo_{3}O_{8}

The linear magnetoelectric effect is an attractive phenomenon in condensed matters and provides indispensable technological functionalities. Here a colossal linear magnetoelectric effect with diagonal component α_{33} reaching up to ∼480  ps/m is reported in a polar magnet Fe_{2}Mo_{3}O_{8}. This effect can persist in a broad range of magnetic field (∼20  T) and is orders of magnitude larger than reported values in literature. Such an exceptional experimental observation can be well reproduced by a theoretical model affirmatively unveiling the vital contributions from the exchange striction, while the sign difference of magnetocrystalline anisotropy can also be reasonably figured out.

Ab Initio Discovery of Stable Double Perovskite Oxides Na2BIO6 (B = Bi, In) with Promising Optoelectronic Properties

Recently, oxide perovskites are garnering tremendous attention from the scientific community as possible alternatives to the currently used active materials in photovoltaic (PV) and photoelectrochemical (PEC) devices. Herein, we report the stability and promising optoelectronic properties of a few previously unexplored periodates A₂BIO₆ (A = alkali metal; B = Bi, Sb, In, Tl, Ga). Our compositional phase diagram analysis reveals two compounds Na₂BIO₆ (B = Bi, In) that stabilize in monoclinic phase at thermodynamic equilibrium, showing band gaps (E_g) in the visible region. Band engineering via alloying Bi in Na₂InIO₆ introduces Bi 6s lone pair bands above the valence band maxima (VBM), while alloying Tl in Na₂BiIO₆ introduces an intermediate band (Tl s character) below the conduction band minima. These alloys, Na₂Bi_0.25In_0.75IO₆ and Na₂Tl_0.25Bi_0.75IO₆, acquire E_g's of 1.66 and 1.78 eV, respectively. Apart from band gap, the antibonding VBM, favorable optical absorption, highly dispersive band edges, and well-positioned VBM (for efficient oxygen evolution reaction) make these compounds highly promising for PV and PEC applications.

Perovskite Oxides Prepared by Hydrothermal and Solvothermal Synthesis: A Review of Crystallisation, Chemistry, and Compositions

Perovskite oxides with general composition ABO₃ are a large group of inorganic materials that can contain a variety of cations from all parts of the Periodic Table and that have diverse properties of application in fields ranging from electronics, energy storage to photocatalysis. Solvothermal synthesis routes to these materials have become increasingly investigated in the past decade as a means of direct crystallisation of the solids from solution. These methods have significant advantages leading to adjustment of crystal form from the nanoscale to the micron-scale, the isolation of compositions not possible using conventional solid-state synthesis and in addition may lead to scalable processes for producing materials at moderate temperatures. These aspects are reviewed, with examples taken from the past decade's literature on the solvothermal synthesis of perovskites with a systematic survey of B-site cations, from transition metals in Groups 4-8 and main group elements in Groups 13, 14 and 15, to solid solutions and heterostructures. As well as hydrothermal reactions, the use of various solvents and solution additives are discussed and some trends identified, along with prospects for developing control and predictability in the crystallisation of complex oxide materials.

Yttrium Manganese Oxide Phase Stability and Selectivity Using Lithium Carbonate Assisted Metathesis Reactions

In solid-state chemistry, stable phases are often missed if their synthesis is impractical, such as when decomposition or a polymorphic transition occurs at relatively low temperature. In the preparation of complex oxides, reaction temperatures commonly exceed 1000 °C with little to no control of the reaction pathway. Thus, a prerequisite for exploring the synthesis of complex oxides is to identify reactions with intermediates that are kinetically competent at low temperatures, as provided by assisted metathesis reactions. Here, we study the assisted metathesis reaction Mn₂O₃ + 2.2YCl₃·6H₂O + 3Li₂CO₃ → 2YMnO₃ + 5.8LiCl + 0.2LiYCl₄ + 3CO₂ using in situ synchrotron X-ray diffraction. By changing the atmosphere, oxygen vs inert gas, the reaction product changes from the overoxidized perovskite YMnO_3+δ to the hexagonal YMnO₃ polymorph at the reaction temperature of 850 °C, respectively. Analysis of the reaction pathways reveals two parallel reaction pathways in forming YMnO₃ phases: (1) the slow reaction of metal oxides in a LiCl flux (Y₂O₃ + Mn₂O₃ [Formula: see text] 2YMnO₃) and (2) the fast reaction from ternary intermediates (YOCl + LiMnO₂ → LiCl + YMnO₃). Control reactions reveal that both proposed pathways in isolation result in product formation, but the direct preparation of ternary intermediates (YOCl + LiMnO₂ → LiCl + YMnO₃) occurs at lower temperatures (500 °C) and shorter times (<24 h) and forms nominally stoichiometric orthorhombic YMnO₃. These ternary intermediates react at a faster rate than the slow stepwise oxygenation of yttrium chloride to Y₂O₃ (YCl₃ → YOCl → Y₃O₄Cl → Y₂O₃), which is relatively inert. These results support a kinetically controlled reaction pathway to form YMnO₃ phases in assisted metathesis reactions with phase selectivity achievable through changes to reaction atmosphere.

Mechanosynthesis of the Whole Y1-xBixMn1-xFexO3 Perovskite System: Structural Characterization and Study of Phase Transitions

Perovskite BiFeO₃ and YMnO₃ are both multiferroic materials with distinctive magnetoelectric coupling phenomena. Owing to this, the Y_1−xBi_x Mn_1−xFe_xO₃ solid solution seems to be a promising system, though poorly studied. This is due to the metastable nature of the orthorhombic perovskite phase of YMnO₃ at ambient pressure, and to the complexity of obtaining pure rhombohedral phases for BiFeO₃-rich compositions. In this work, nanocrystalline powders across the whole perovskite system were prepared for the first time by mechanosynthesis in a high-energy planetary mill, avoiding high pressure and temperature routes. Thermal decomposition temperatures were determined, and structural characterization was carried out by X-ray powder diffraction and Raman spectroscopy on thermally treated samples of enhanced crystallinity. Two polymorphic phases with orthorhombic Pnma and rhombohedral R3c h symmetries, and their coexistence over a wide compositional range were found. A gradual evolution of the lattice parameters with the composition was revealed for both phases, which suggests the existence of two continuous solid solutions. Following bibliographic data for BiFeO₃, first order ferroic phase transitions were located by differential thermal analysis in compositions with x ≥ 0.9. Furthermore, an orthorhombic-rhombohedral structural evolution across the ferroelectric transition was characterized with temperature-dependent X-ray diffraction.

Oxygen storage properties of hexagonal HoMnO3+δ

Structural and oxygen content changes of hexagonal HoMnO_3+δ manganite at the stability boundary in the perovskite phase have been studied by X-ray diffraction and thermogravimetry using in situ oxidation and reduction processes at elevated temperatures in oxygen and air.

Influence of Fe substitution on the Jahn-Teller distortion and orbital anisotropy in orthorhombic Y(Mn1-xFex)O3 epitaxial films

Multiferroic YMn1-xFexO3(020) (x = 0.125, 0.25, 0.50) epitaxial thin films with an orthorhombic structure (space group Pbnm) were prepared on a YAlO3(010) substrate by pulsed-laser deposition. Upon Fe substitution, the b-axis was clearly shortened, whereas the a- and c-axes were slightly lengthened based on XRD analysis. To understand the influence of orbital polarization and the Jahn-Teller effect of Mn(3+) on Fe substitution and also the local octahedral-site distortion of Fe(3+) in an environment of Jahn-Teller-active Mn(3+) ions in YMn1-xFexO3 films, we measured the polarization-dependent X-ray absorption spectra at the Mn-L2,3 and Fe-L2,3 edges, and also simulated the experimental spectra using configuration-interaction multiplet calculations. Although Δeg for the Mn(3+) ion decreased from 0.9 eV in pure YMnO3 to 0.6 eV in the half-Fe-substituted sample, a single eg electron was still strongly constrained to the d3y(2)-r(2) orbital for all the Fe concentrations tested. The largest Δeg, 0.5 eV, for the Fe(3+) ion was derived for a sample with 12.5% Fe substitution, and gradually decreased to 0.15 eV for the half-Fe-substituted sample. The local octahedral-site distortion of the Fe(3+) ion inside the YMnO3 lattice was similar to that of the Mn(3+) ion, whereas the Jahn-Teller distortion and GdFeO3-type distortion of the Mn(3+) ion were decreased by the spherical high-spin Fe(3+) ions. The combination of the experimental and theoretical data provides both profound insight into the variation of the Jahn-Teller distortion and orbital anisotropy and instructive information about the magnetic structures in these orthorhombic YMn1-xFexO3 thin films.

Pressure effect on the properties of magnetic moments and phase transitions in YMnO3 from first principles

We report the properties of magnetic, electronic, phonon frequencies and magnetic phase transitions in orthorhombic perovskite YMnO₃ by means of first-principles calculations.

Multiferroicity and Magnetoelectric Coupling in TbMnO3 Thin Films

In this work, we report the growth and functional characterizations of multiferroic TbMnO3 thin films grown on Nb-doped SrTiO3 (001) substrates using pulsed laser deposition. By performing detailed magnetic and ferroelectric properties measurements, we demonstrate that the multiferroicity of spin origin known in the bulk crystals can be successfully transferred to TbMnO3 thin films. Meanwhile, anomalous magnetic transition and unusual magnetoelectric coupling related to Tb moments are observed, suggesting a modified magnetic configuration of Tb in the films as compared to the bulk counterpart. In addition, it is found that the magnetoelectric coupling enabled by Tb moments can even be seen far above the Tb spin ordering temperature, which provides a larger temperature range for the magnetoelectric control involving Tb moments.

Synthesis of perovskite-type manganites Yb1−xDyxMnO3 (0.1 ≤ x ≤ 0.5) via solid-state reaction and high-pressure flux methods followed by structural characterization and magnetic property studies

h-Yb_1−xDy_xMnO₃ (0.1 ≤ x ≤ 0.5) and single crystal o-Yb_0.5Dy_0.5MnO₃ were firstly synthesized, and o-Yb_0.5Dy_0.5MnO₃ has the paramagnetic property due to slight structural difference.

Structural characterization and multiferroic properties of hexagonal nano-sized YMnO3 developed by a low temperature precursor route

The highest surface area was achieved and room temperature ferroelectricity with ferromagnetic interactions appeared in the as-prepared YMnO₃ nanoparticles.

High pressure and multiferroics materials: a happy marriage

The community of material scientists is strongly committed to the research area of multiferroic materials, both for the understanding of the complex mechanisms supporting the multiferroism and for the fabrication of new compounds, potentially suitable for technological applications. The use of high pressure is a powerful tool in synthesizing new multiferroic, in particular magneto-electric phases, where the pressure stabilization of otherwise unstable perovskite-based structural distortions may lead to promising novel metastable compounds. The in situ investigation of the high-pressure behavior of multiferroic materials has provided insight into the complex interplay between magnetic and electronic properties and the coupling to structural instabilities.