Series Of Double Perovskites Research Articles

High-pressure stabilisation of R = Y member of R2CuTiO6 double perovskite series

Double perovskite oxides of the A2B’B″O6 type with Jahn-Teller active Cu2+ as the B′ constituent have gained considerable research interest in recent years. For fundamental studies, the rare earth element (R) based systems such as R2CuTiO6 form an intriguing research platform as they allow systematic chemical-pressure studies by simply controlling the size of the R constituent. However, for the R2CuTiO6 compounds conventional ambient-pressure high-temperature synthesis yields an orthorhombic (Pnma) double perovskite structure for the largest R constituents (La–Gd) only, while the compounds with the smaller R:s adopt a hexagonal structure. Here we demonstrate a hexagonal-to-perovskite structure conversion for the R ​= ​Y compound achieved through a high-pressure (HP) high-temperature treatment at 4 ​GPa and 1000 ​°C. Structural details of the thus stabilized new double perovskite phase of Y2CuTiO6 are addressed through a combined DFT simulation and Rietveld refinement study, revealing signs towards the rare layered-type ordering of the B-site (Cu and Ti) cations. Similar to the previously reported R2CuTiO6 perovskite phases with R ​= ​La, Pr, and Nd, the R ​= ​Y member is found paramagnetic throughout the measured temperature range of 5–300 ​K. From UV–vis absorption measurements the optical bandgap is estimated to be ca 3.4 ​eV.

Effects of chemically induced cationic disturbance on Mn4+ luminescence in double perovskites - temperature and pressure experimental and computational studies

We show the opportunity for tuning of the spectral position of the Mn4+ red emission in the series of double perovskites, Ba2LaNbO6:Mn4+, Ba2La(Nb0.8,Zr0.1,W0.1)O6:Mn4+, and Ba2La(Zr0.5,W0.5)O6:Mn4+ with increasing chemically induced symmetry disturbance. Such a disorder appeared attractive to engineering phosphors for pressure sensors or horticultural applications, for instance. The goal of the present research, not yet systematically addressed in the literature, was to unveil the correlation between chemically induced controlled crystal lattice distortion and the luminescence of Mn4+. For this purpose, the luminescence of these phosphors was methodically investigated at different pressures and temperatures. A pressure-induced redshift of photoluminescent lines with the rate of − 4 cm−1/kbar was found within the 0–230 kbar range, and the emission peak moved from 685 to 740 nm then. Furthermore, the cationic disorder allowed tuning of the Mn4+ luminescence making it useful for horticultural applications with a better fit between the emission wavelength and the strong chlorophyll absorption in the deep red part of the spectrum. The Mn4+ energy levels were computationally determined using the exchange charge model of the crystal-field theory which allowed for a deeper understanding of the experimental results. We found a correlation between the introduced disorder of the cationic subsystem and the energy of the Mn4+ emitting 2Eg level (R-line) as well as its intensity. This research brought a deeper understanding of the Mn4+-activated phosphors and, in turn, provides tips for a prudent search of materials for advanced practical uses.

High-Pressure Stabilisation of R = Y Member of R2cutio6 Double Perovskite Series

High-Pressure Stabilisation of R = Y Member of R2cutio6 Double Perovskite Series

Ferro-octupolar Order and Low-Energy Excitations ind2Double Perovskites of Osmium

Conflicting interpretations of experimental data preclude the understanding of the quantum magnetic state of spin-orbit coupled $d^2$ double perovskites. Whether the ground state is a Janh-Teller-distorted order of quadrupoles or the hitherto elusive octupolar order remains debated. We resolve this uncertainty through direct calculations of all-rank inter-site exchange interactions and inelastic neutron scattering cross-section for the $d^2$ double perovskite series Ba$_2M$OsO$_6$ ($M$= Ca, Mg, Zn). Using advanced many-body first principles methods we show that the ground state is formed by ferro-ordered octupoles coupled by superexchange interactions within the ground-state $E_g$ doublet. Computed ordering temperature of the single second-order phase-transition is consistent with experimentally observed material-dependent trends. Minuscule distortions of the parent cubic structure are shown to qualitatively modify the structure of gaped magnetic excitations.

Chemically Localized Resonant Excitons in Silver-Pnictogen Halide Double Perovskites.

Halide double perovskites with alternating silver and pnictogen cations are an emerging family of photoabsorber materials with robust stability and band gaps in the visible range. However, the nature of optical excitations in these systems is not yet well understood, limiting their utility. Here, we use ab initio many-body perturbation theory within the GW approximation and the Bethe–Salpeter equation approach to calculate the electronic structure and optical excitations of the double perovskite series Cs2AgBX6, with B = Bi3+, Sb3+ and X = Br–, Cl–. We find that these materials exhibit strongly localized resonant excitons with energies from 170 to 434 meV below the direct band gap. In contrast to lead-based perovskites, the Cs2AgBX6 excitons are computed to be non-hydrogenic with anisotropic effective masses and sensitive to local field effects, a consequence of their chemical heterogeneity. Our calculations demonstrate the limitations of the Wannier–Mott and Elliott models for this class of double perovskites and contribute to a detailed atomistic understanding of their light–matter interactions.

Evolution of transition metal charge states in correlation with the structural and magnetic properties in disordered double perovskites Ca2-xLaxFeRuO6 (0.5 ≤ x ≤ 2).

A series of disordered Ca1.5La0.5FeRuO6, CaLaFeRuO6 and La2FeRuO6 double perovskites were prepared by the solid-state reaction method and investigated by neutron powder diffraction, X-ray absorption near-edge structure (XANES) analysis at the Ru-K edge, Mössbauer spectroscopy, DC magnetization and resistivity measurements. All compounds crystallize in the orthorhombic crystal structure with the space group Pbnm down to 3 K, showing a random distribution of Fe and Ru at the B site. Thermogravimetric analysis indicates oxygen deficiency in the Ca-rich and formal oxygen hyperstoichiometry in the La-rich members of the present series. While Mössbauer spectra verify the Fe3+ state for all compositions, the XANES study reveals a variable Run+ oxidation state which decreases with increasing La content. The end member actually is a Ru3+/Ru4+ compound with possibly some cation vacancies. From magnetic susceptibility and neutron diffraction measurements, the presence of a G-type antiferromagnetic ordering was observed with a drastic increase in transition temperature from 275 K (Ca1.5La0.5FeRuO6) to 570 K (La2FeRuO6). Mössbauer spectroscopy confirms the presence of long-range ordering but, due to local variations in the exchange interactions, the magnetic states are microscopically inhomogeneous. All the samples are variable range hopping semiconductors. A complex interplay between structural features, charge states, anion or cation defects, and atomic disorder determines the magnetic properties of the present disordered 3d/4d double perovskite series.

Electronic properties and crystal structures of double-perovskites, Ba2BiIIIBiVO6,Ba2PrBiO6, and Ba2PrSbO6: First-principles study

In recent experiments, a significant band gap widening was observed when Sb was substituted for Bi in the double-perovskite Ba2PrBiO6. In this work, we study a series of double-perovskites, Ba2BiIIIBiVO6, Ba2PrBiO6, and Ba2PrSbO6 using the first-principles density functional theory with the Heyd-Scuseria-Ernzerhof hybrid functional to investigate the substitution effect on the structural and electronic properties. We find that the two topmost valence bands are disappeared on the substitution of PrIII for BiIII, and the two bottommost conduction bands are disappeared on the substitution of SbV for BiV, causing the significant band gap widening. Further, our calculation suggests that the Ba2PrPrBiO6 is a possible candidate as a source of the PrIV signal observed in the experiment. We find that the B-site disordering atomic configuration, Ba2B″VB′IIIO6, are restored to those of the original structures. On the other hand, our results also suggest the importance of the partial B-site disorder to explain the experimentally observed band gaps.

Complex magnetic properties in the mixed 4f−5d double perovskite iridates X2ZnIrO6(X=Nd,Sm,Eu,Gd)

In this paper, we report on the synthesis and magnetic properties of a series of double perovskites $\mathit{Ln}{}_{2}{\mathrm{ZnIrO}}_{6}$ with $\mathit{Ln}$ = Nd, Sm, Eu, Gd. These compounds present examples of the rare case of double perovskites (general formula $A{}_{2}BB{}^{\ensuremath{'}}{\mathrm{O}}_{6}$) with a magnetic $4f$ ion on the $A$ site in combination with the strongly spin-orbit coupled 5d transition-metal ion ${\mathrm{Ir}}^{4+}$ on the $B$ sublattice. We discuss the impact of different rare earths on the macroscopic magnetic properties. ${\mathrm{Gd}}_{2}{\mathrm{ZnIrO}}_{6}$ and ${\mathrm{Eu}}_{2}{\mathrm{ZnIrO}}_{6}$ show ferrimagnetic or canted antiferromagnetic order below ${T}_{N}$ = 23 and 12 K, respectively. ${\mathrm{Sm}}_{2}{\mathrm{ZnIrO}}_{6}$ orders antiferromagnetically at ${T}_{N}$ = 13 K. ${\mathrm{Nd}}_{2}{\mathrm{ZnIrO}}_{6}$ exhibits more complex magnetic properties with a strong field dependence ranging from a two-step spin reorientation at ${\ensuremath{\mu}}_{0}H$ = 0.01 T to an antiferromagnetic ground state at intermediate external fields to a spin-flop phase for ${}_{0}H \ensuremath{\ge}$ 4 T. This unique behavior suggests an interesting interplay between ${\mathrm{Nd}}^{3+}$ and ${\mathrm{Ir}}^{4+}$. To further shed light on the relevant magnetic interaction, the zero-field magnetic ground state of ${\mathrm{Nd}}_{2}{\mathrm{ZnIrO}}_{6}$ is examined via neutron powder diffraction. In general, the magnetic properties of $\mathit{Ln}{}_{2}{\mathrm{ZnIrO}}_{6}$ hint towards a substantial contribution of the rare-earth ions and a significant correlation between $5d$ and $4f$ magnetism.

Exchange Interactions Mediated by Nonmagnetic Cations in Double Perovskites.

Establishing the physical mechanism governing exchange interactions is fundamental for exploring exotic phases such as quantum spin liquids in real materials. In this Letter, we address exchange interactions in Sr_{2}CuTe_{x}W_{1-x}O_{6}, a series of double perovskites that realize a spin-1/2 square lattice and are suggested to harbor a quantum spin liquid ground state arising from the random distribution of nonmagnetic ions. Our abinitio multireference configuration interaction calculations show that replacing Te atoms with W atoms changes the dominant couplings from nearest to next-nearest neighbor due to the crucial role of unoccupied states of the nonmagnetic ions in the super-superexchange mechanism. Combined with spin-wave theory simulations, our calculated exchange couplings provide an excellent description of the inelastic neutron scattering spectra of the parent compounds, as well as explaining that the magnetic excitations in Sr_{2}CuTe_{0.5}W_{0.5}O_{6} emerge from bond-disordered exchange couplings. Our results demonstrate the crucial role of the nonmagnetic cations in exchange interactions paving the way to further explore quantum spin liquid phases in bond-disordered materials.

Copper(I)-Based Highly Emissive All-Inorganic Rare-Earth Halide Clusters

Summary The development of new environmentally friendly luminescent materials is crucial for future solid-state lighting, sensor, and display applications. Here, a Cu(I)-based all-inorganic rare-earth halide material, Rb 8 CuSc 3 Cl 18 , has been synthesized by a solid-state reaction method. In this compound, two Cu(I) ions are connected to three rare-earth halide octahedra to form a paddle-wheel-like cluster. The Cu(I) coordinated rare-earth halide clusters contribute to a strong blue photoluminescence emission. This Cu(I)-regulated emission can be extended to other isostructural compounds, such as Rb 8 CuY 3 Cl 18 . Moreover, the crucial role of Cu(I) has been illustrated by the isostructural non-emissive Rb 8 AgSc 3 Cl 18 . On the basis of comprehensive spectroscopy studies and density functional theory calculations, we found that Cu(I) photo-oxidation and correct orbital-energy-level alignment are crucial for the observed bright-blue emission through a proposed metal (Cu)-to-octahedra ([ScCl 6 ] 3− ) charge-transfer mechanism. The discovery of Cu(I)-based all-inorganic rare-earth halide clusters establishes a new strategy for constructing promising emissive halide materials.

Crystal Structures and Phase-Transitions Analysis of the Double Perovskites Sr2Co1−xNixTeO6 (x = 0.25, 0.5 and 0.75) Using X-ray Powder Diffraction, Raman and Infrared Spectroscopy

The reaction between the complexes of double perovskite formula Sr2Co1−xNixTeO6 in different stoichiometric proportions (x = 0.25, 0.5 and 0.75) have been processed in polycrystalline form by solid– state reaction mode in air. Based on the Rietveld refinements of x-ray powder diffraction data, the crystal structures and phase transitions, at room temperature of this double perovskite series are reported. The materials crystallize in a monoclinically distorted perovskite structure (the two compositions with x = 0.5 and 0.75 belong the to I2/m space group, while the composition with x = 0.25 crystallize in P21/n space group). We found a good agreement between the lattice parameters of this series and those of the two materials Sr2CoTeO6 and Sr2NiTeO6 with x = 0 and 1, respectively. The linear evolution of crystalline parameters proves the realization of the Vegard Law. The effect of the partial substitution of Co by Ni was also seen in the spectra of Raman and infrared, where a band shift was observed with increased nickel content.

Correlation between composition, electrical and electrochemical properties of LnCo1-xCrxO3 (Ln = Pr, Gd and x = 0, 0.5 and 1) perovskites

Electrical and electrocatalytic properties of two series of double perovskites, LnCo1-xCrxO3 (Ln = Pr, Gd, and x = 0, 0.5 and 1), were investigated and discussed in the light of perovskite composition. Studied perovskites were synthesized by the solution combustion method, and powder XRD patterns showed that all compounds crystallize in the GdFeO3-structure type. The morphology of perovskite crystals was studied by SEM, whereas obtained microphotographs implied porous microstructure. The conductivity of both perovskite series spanned in the range of semiconductors as revealed from electrical measurements. The electrocatalytic activity toward oxygen evolution reaction, oxidation of hydrogen peroxide, and methanol was studied in alkaline solutions by cyclic voltammetry. The influence of electronic, structural and morphological factors to the electrical and electrocatalytic properties is discussed. The praseodymium series showed higher electrocatalytic activity than the gadolinium one, while the most pronounced activity was detected for PrCoO3.

Synchrotron X-ray diffraction study of double perovskites Sr2RNbO6 (R = Sm, Gd, Dy, Ho, Y, Tm, and Lu)

A series of double-perovskite oxides, Sr2RNbO6 (R = Sm, Gd, Dy, Ho, Y, Tm, and Lu) were prepared and their crystal structure and powder diffraction reference patterns were determined using the Rietveld analysis technique. The crystal structure of each of the Sr2RNbO6 phase is reported in this paper. The R = Gd, Ho, and Lu samples were studied using synchrotron radiation, while R = Sm, Dy, Y, and Tm samples were studied using laboratory X-ray diffraction. Members of Sr2RNbO6 are monoclinic with a space group of P21/n and are isostructural with each other. Following the trend of “lanthanide contraction”, from R = Sm to Lu, the lattice parameters “a” of these compounds decreases from 5.84672(10) to 5.78100(3) Å, b from 5.93192(13) to 5.80977(3) Å, c from 8.3142(2) to 8.18957(5) Å, and V decreases from 288.355(11) to 275.057(2) Å3. In this double-perovskite series, the R3+ and Nb5+ ions are structurally ordered. The average Nb–O bond length is nearly constant, while the average R–O bond length decreases with the decreasing ionic radius of R3+. Powder diffraction patterns for these compounds have been submitted to the Powder Diffraction File (PDF).

Influence of Ca-doping in layered perovskite PrBaCo2O5+δ on the phase transition and cathodic performance of a solid oxide fuel cell

We investigated the phase transition and its correlated electrical and electro-chemical properties of a novel double perovskite series, PrBa1−xCaxCo2O5+δ.

Sol gel and ceramic synthesis of Sr2FeMo1−xWxO6 (0 ≤ x ≤ 1) double perovskites series

Optimization of pure phase double perovskite series via sol–gel methods.

Structural and Magnetic Investigation of the Double-Perovskite Ba2Co1−x Fe x ReO6 (0 ≤ x ≤ 0.5)

Double-perovskite series of Ba2Co1−xFexReO6 (x = 0, 0.2, 0.4, and 0.5) were prepared as single-phase materials using the conventional solid-state reaction method and studied by X-ray powder diffraction and magnetization techniques. The Rietveld analysis of the X-ray diffraction patterns showed a partial disordering in the Re and Fe/Co layers on the B sites of the double perovskites, which played a central role in the structural and magnetic properties of the compounds. The findings showed that symmetry was cubic (Fm3m) for all of the samples. The magnetization versus temperature measurements at H = 500 Oe revealed that the Ba2CoReO6 and Ba2Co0.8Fe0.2ReO6 samples showed antiferromagnetic state and exhibited a paramagnetic–ferromagnetic transition for x = 0.4 and 0.5. The Curie temperature was also noted to increase with the increase in the Fe content.

Structural phase transitions and magnetic and spectroscopic properties of the double perovskites Sr2Co1-xMgxTeO6 (x = 0.1, 0.2 and 0.5).

The structural and magnetic properties of a series of ordered double perovskites with the formula Sr(2)Co(1-x)Mg(x)TeO(6) (x = 0.1, 0.2 and 0.5) are investigated by X-ray diffraction, low temperature neutron diffraction, electron paramagnetic resonance and magnetic susceptibility. The progressive substitution of the paramagnetic Co(2+) high spin ion by the diamagnetic Mg(2+), of about the same size, induces changes in the room temperature crystal structure, from a distorted P2(1)/n phase for the undoped Sr(2)CoTeO(6) oxide to the I4/m of the end member (Sr(2)MgTeO(6)). These perovskites experience structural transitions on heating, the temperature at which the transitions occur being smaller as x increases. The novel approach of mode-crystallography is used for the analysis. All oxides show antiferromagnetic exchange interactions between Co(2+) ions but the long range antiferromagnetic order is not achieved for the phase with x = 0.5. The low temperature neutron diffraction data have been evaluated using a full symmetry analysis. Results are consistent with an unquenched orbital contribution of a high spin Co(2+) ion.

X-ray diffraction study and powder patterns of double-perovskites Sr2RSbO6 (R = Pr, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Tm, Yb, and Lu)

The X-ray diffraction powder patterns were prepared and the crystal structures were refined for the double-perovskite series of compounds, Sr2RSbO6 (R = Pr, Nd, Sm, Eu, Gd, Dy, Ho, Y, Er, Tm, Yb, and Lu). We found the structures of the entire Sr2RSbO6 series to be monoclinic with space group P21/n (no. 14), and Z = 2. From R = Lu to Pr, the lattice parameters “a” range from 5.7779(2) to 5.879 05(8) Å, “b” range from 5.7888(2) to 5.969 52(9) Å, “c” range from 8.1767(3) to 8.369 20(12) Å, “β” range from 90.112(2)° to 90.313(1)°, and “V” range from 273.483(4) to 293.714(7) Å3. These lattice parameters follow the well-established trend of “lanthanide contraction”. The R3+ and Sb5+ ions are found to be fully ordered in the double-perovskite arrangement of alternating corner-sharing octahedra in a zigzag fashion. The SrO12, RO6, and SbO6 cages are all found to have distorted coordination environments. Powder diffraction patterns of these compounds have been prepared, submitted, and published in the Powder Diffraction File.

Structural, electronic and magnetic properties of the series of double perovskites [formula omitted

Polycrystalline samples of the series of double perovskites Sr2−xLaxFeIrO6 were synthesized. Their structural, electronic and magnetic properties were investigated by X-ray powder diffraction, Mössbauer spectroscopy, magnetic susceptibility, heat capacity and electrical resistivity experiments. The compounds crystallize in a monoclinic structure and were fitted in space group P21/n, with a significant degree of Fe/Ir cationic disorder. As in Ca2−xLaxFeIrO6 the Sr-based system seems to evolve from an antiferromagnetic ground state for the end members (x=0.0 and x=2.0) to a ferrimagnetic order in the intermediate regions (x~1). Since Mössbauer spectra indicate that Fe valence remains 3+ with doping, this tendency of change in the nature of the microscopic interaction could be attributed to Ir valence changes, induced by La3+ electrical doping. Upon comparing both Ca and Sr series, Sr2−xLaxFeIrO6 is more structurally homogenous and presents higher magnetization and transition temperatures. Magnetic susceptibility measurements at high temperatures on Sr1.2La0.8FeIrO6 indicate a very high ferrimagnetic Curie temperature TC~700K. For the Sr2FeIrO6 compound, electrical resistivity experiments under applied pressure suggest that this material might be a Mott insulator.

Origin of magnetism and trend inTcin Cr-based double perovskites: Interplay of two driving mechanisms

Employing first principles density functional calculations, together with solution of the low-energy, model Hamiltonian constructed in a first principles manner, we explored the origin of magnetism and the ${T}_{c}$ trend in Cr-based double perovskite series, Sr${}_{2}$Cr${B}^{\ensuremath{'}}$O${}_{6}$ (${B}^{\ensuremath{'}}=$ W/Re/Os). Our study shows that the apparently puzzling ${T}_{c}$ trend in Sr${}_{2}$Cr${B}^{\ensuremath{'}}$O${}_{6}$ (${B}^{\ensuremath{'}}=$ W/Re/Os) series can be understood in terms of the interplay of the hybridization driven mechanism and the superexchange mechanism.