Double Perovskite Sr Research Articles

Near-infrared luminescence from double-perovskite Sr<sub>3</sub>Sn<sub>2</sub>O<sub>7</sub>:Nd<sup>3+</sup>: A new class of probe for in vivo imaging in the second optical window of biological tissue

Near-infrared luminescence from double-perovskite Sr<sub>3</sub>Sn<sub>2</sub>O<sub>7</sub>:Nd<sup>3+</sup>: A new class of probe for in vivo imaging in the second optical window of biological tissue

Time-reversal-breaking topological phases in antiferromagnetic Sr2FeOsO6 films

In this work, we studied time-reversal-breaking topological phases as a result of the interplay between antiferromagnetism and inverted band structures in thin films of antiferromagnetic double perovskite transition-metal Sr$_2$FeOsO$_6$. By combining the first-principles calculations and analytical models, we demonstrate that the quantum anomalous Hall phase and chiral topological superconducting phase can be realized in this system. We find that to achieve time-reversal-breaking topological phases in antiferromagnetic materials, it is essential to break the combined symmetry of time reversal and inversion, which generally exists in antiferromagnetic structures. As a result, we can utilize an external electric gate voltage to induce the phase transition between topological phases and trivial phases, thus providing an electrically controllable topological platform for the future transport experiments.

Quantitative STEM Imaging of Order-Disorder Phenomena in Double Perovskite Thin Films.

Using aberration-corrected high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), we investigate ordering phenomena in epitaxial thin films of the double perovskite Sr_{2}CrReO_{6}. Experimental and simulated imaging and diffraction are used to identify antiphase domains in the films. Image simulation provides insight into the effects of atomic-scale ordering along the beam direction on HAADF-STEM intensity. We show that probe channeling results in ±20% variation in intensity for a given composition, allowing 3D ordering information to be probed using quantitative STEM.

Weak orbital ordering of Irt2gstates in the double perovskiteSr2CeIrO6

The electronic and magnetic properties of monoclinic double perovskite Sr$_2$CeIrO$_6$ were examined based on both experiments and first-principles density functional theory calculations. From the calculations we conclude that low-spin-state Ir$^{4+}$ (5$\textit{d}^5$, S=$\frac{1}{2}$) shows t$_{2g}$ band derived anti-ferro type orbital ordering implying alternating occupations of $\textit{d}_{yz}$ and $\textit{d}_{xz}$ orbitals at the two symmetrically independent Ir sites. The experimentally determined Jahn-Teller type distorted monoclinic structure is consistent with the proposed orbital ordering picture. Surprisingly, the Ir-5$\textit{d}$ orbital magnetic moment was found to be $\approx$ 1.3 times larger than the spin magnetic moment. The experimentally observed AFM-insulating states are consistent with the calculations. Both electron-electron correlation and spin-orbit coupling (SOC) are required to drive the experimentally observed AFM-insulating ground state. This single active site double perovskite provides a rare platform with a prototype geometrically frustrated fcc lattice where among the different degrees of freedom (i.e spin, orbital, and lattice), spin-orbit interaction and Coulomb correlation energy scales compete and interact with each other.

Structural and magnetic properties of the5d2double perovskitesSr2BReO6(B=Y, In)

We have performed magnetic susceptibility, heat capacity, neutron powder diffraction, and muon spin relaxation experiments to investigate the magnetic ground states of the 5$d^2$ double perovskites Sr$_2$YReO$_6$ and Sr$_2$InReO$_6$. We find that Sr$_2$YReO$_6$ is a spin glass, while Sr$_2$InReO$_6$ hosts a non-magnetic singlet state. By making detailed comparisons with other 5$d^2$ double perovskites, we argue that a delicate interplay between spin-orbit coupling, non-cubic crystal fields, and exchange interactions plays a key role in the great variation of magnetic ground states observed for this family of materials.

Magnetic structure of theS=12quasi-two-dimensional square-lattice Heisenberg antiferromagnetSr2CuTeO6

The magnetic structure of the double perovskite compound Sr$_2$CuTeO$_6$ was determined from neutron powder diffraction data. This material is magnetically described as an $S\,{=}\,1/2$ quasi-two-dimensional square-lattice Heisenberg model with antiferromagnetic nearest-neighbor and next-nearest-neighbor interactions. Sr$_2$CuTeO$_6$ undergoes a magnetic phase transition at $T_{\rm N}\,{\simeq}\,29\,$ K. The spin structure below $T_{\rm N}$ is N\'{e}el antiferromagnetic on the square lattice, which means that the nearest-neighbor interaction ($J_1$) is stronger than the next-nearest-neighbor interaction ($J_2$), in contrast to other isostructural compounds such as Ba$_2$CuWO$_6$ and Sr$_2$CuWO$_6$, for which $|J_1|\,{<}\,|J_2|$ is realized.

Effect of Quench Treatment on Fe/Mo Order and Magnetic Properties of Double Perovskite Sr2FeMoO6**Supported by the National Natural Science Foundation of China under Grant No U1304110, and the Doctoral Science Foundation of Henan Normal University under Grant No 01026500109.

A quench-treatment technique is used to prepare a high-quality polycrystalline sample of double perovskite Sr2 FeMoO6 (SFMO). X-ray powder diffraction analysis reveals that the sample has a single phase and exhibits I4/m symmetry. The cation order η of the sample increases to 98.9(2)% from 94.2(3)%, which is prepared by the traditional sol-gel method. The initial magnetization isotherm of the sample is detected at 300 K. Unit-cell magnetization for the current sample is 1.332 μB at 300 K, and the one for the traditional sol-gel method sample is 0.946 μB. Unit-cell magnetization is enhanced to 40.80% by the quench-treatment technique. Quench treatment is an effective method of enhancing the Fe/Mo order and magnetic properties of double perovskite SFMO.

Perovskite-Type Thin Slabs: A First-Principles Study of Their Magnetic and Electronic Properties

The development of spintronic devices is the most promising and interesting way to improve conventional electronics. They will allow us to continue diminishing the devices' dimensions as well as optimizing the energy requirements for their operation. Perovskites stand out among materials that could be used in those devices because their variety permits combinations of optical, electronic, and magnetic properties. The bulk double perovskite Sr 2FeMoO6 (SFMO) is a half-metallic system that has become very attractive after the Kobayashi report about their high Curie temperature (about 470 K). SFMO has been used to build solid oxide fuel cell electrodes, but this compound could be used as a laminar system in the development of spintronic devices because of its high spin polarization. This proposal has been motivated by the exploitation of the magnetoresistive response in manganite applications and the reported experimental work on perovskite thin films. The inclusion of SFMO laminar systems in spintronic devices could affect magnetic-tunnel-junction-like devices. From a crystalline SFMO model system, thin slabs were excised and a supercell was built for each system, setting the appropriate initial separation between image slabs along the [001] direction. The geometry optimization and magnetic and electronic properties (density of states, band structures, and magnetic moment distribution) were calculated in the density functional theory scheme using the local density approximation with the Hubbard parameter (LDA + U).

The defect structure and chemical lattice strain of the double perovskites Sr2BMoO6-δ (B = Mg, Fe).

The defect structure of B-site ordered double perovskites Sr2BMoO6-δ was analyzed. The defect structure model was proposed and successfully verified using data on oxygen nonstoichiometry of Sr2MgMoO6-δ and Sr2FeMoO6-δ. As a result, equilibrium constants of the defect reactions involved were estimated. Fe and Mo in Sr2FeMoO6-δ were found to be in the mixed oxidation state close to +2.5 and +5.5, respectively. Chemical strain of the Sr2FeMoO6-δ double perovskite lattice was studied by in situ high temperature XRD at 1100 °C depending on pO2. Parameter a of the Sr2FeMoO6-δ cubic cell was found to increase with decreasing pO2 because of lattice chemical expansion. The tetragonal polymorph of Sr2FeMoO6-δ was shown to exhibit transversal isotropy with respect to chemical expansion. It was also found that its crystal lattice expands in the ab-plane and simultaneously contracts along the c-axis when the oxygen content in the double perovskite decreases. In order to describe the degree of anisotropy of chemical strain a new phenomenological coefficient was introduced. This coefficient was shown to affect both the magnitude and change direction of an oxide cell volume caused by its reduction/oxidation. Excellent agreement between the chemical expansion along the a-axis calculated for both polymorphs of Sr2FeMoO6-δ according to the model recently developed and that measured experimentally was shown. Chemical contraction observed along the c-axis with a decreasing oxygen content in the tetragonal polymorph was also found to coincide completely with that calculated using the approach developed in the present study.

The effect of partial substitution of Ni by Mg on the structural, magnetic and spectroscopic properties of the double perovskite Sr2NiTeO6

In this report, the structural, magnetic and spectroscopic properties of the freeze-drying synthesized Sr2Ni1-xMgxTeO6 (x = 0.0, 0.1, 0.2, 0.3 and 0.5) oxides are analyzed by means of X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD), electron paramagnetic resonance, diffuse reflectance and magnetic susceptibility. The XRPD and NPD data analysis using the mode-crystallography approach have revealed that at room temperature (RT), all the compositions are monoclinically distorted with the space group I2/m. The high and low temperature analyses have shown that these materials suffer a series of three structural phase transitions. The EPR results have shown that the spectra of all the compositions are centred at g≈ 2.28, indicating a slightly distorted octahedral environment of Ni(2+), which is in agreement with the crystal structure analysis. The increase of the Mg(2+) content in Sr2Ni1-xMgxTeO6, provokes a decrease of the dipolar interaction effects and thus, the resonance becomes narrower. This resonance does not completely disappear which leads to the idea that the long-range magnetic order is not completely established when x≥ 0.3. The substitution of the Ni(2+) (S = 1) ions by Mg(2+) (S = 0) ions, also induces a weakening of the antiferromagnetic interactions, which is reflected in the diminishing of the absolute value of θ and the Néel temperature TN. The magnetic structure determination revealed the existence of an antiferromagnetic coupling for x- and z-spin components of the nickel atoms.

La and Co doping effects on magnetoresistance of double perovskite Sr2FeMoO6

Double perovskite Sr 2 FeMoO 6 (SFMO) with composition of Sr 2-x La x Fe 1-y Co y MoO 6(x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 at.%; y = 0, 0.05, 0.1, 0.2, 0.3, 0.5, 0.9 at.%) was synthesized by high energy ball milling and sintering. The sintered samples were investigated by means of X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and magnetic measurements. XRD results show that all the samples have single phase double perovskite structure. EDS spectrum confirmed that the actual composition of prepared samples is in agreement with nominal ones. With the increase of doping concentration of La, the magnetization decreases, whereas Curie temperature increases in SFMO. And with doping concentration of La, the magnetoresistance (MR) ratio with a low magnetic field of 480 kA/m increases, has its maximum value as 5% for x = 0.3 at 293 K. The degree of antisite disorder decreases with Co 2+ doping, and therefore results in increase of MR ratio. At room temperature, the MR ratio with a considerable low magnetic field for x = 0.3, y = 0.1 has maximum value as 6.5%.

Synthesis, structure, and magnetic properties of novel B-site ordered double perovskites, SrLaMReO6 (M = Mg, Mn, Co and Ni).

Four new double perovskites, SrLaMReO(6) (M = Mg, Mn, Co, Ni) in which Re(5+) (5d(2)) is present, were prepared via conventional solid state reactions and characterized by X-ray and neutron powder diffraction, XANES, SQUID magnetometry, and muon spin relaxation (μSR). Synchrotron X-ray and neutron diffraction experiments confirmed that all compounds crystallize in the monoclinic P2(1)/n structure type, which consists of alternately corner-shared octahedra of MO(6) and ReO(6). Rietveld refinement results indicated anti-site mixing of less than 7% on the M/Re sites. Bond valence sum calculations (BVS) suggest all M and Re ions are 2+ and 5+, respectively, and for the Mn-containing phase this is also supported by XANES measurements. All of the materials are paramagnetic at room-temperature and their Curie-Weiss temperatures are positive (except for Mg) indicating net ferromagnetic interactions. No evidence for long-range magnetic order is evident in the dc magnetic susceptibility and μSR measurements for SrLaMgReO(6) to 2 K. The Mn-phase shows long-range order at T(C) = 190 K and neutron diffraction revealed a ferromagnetic structure with a refined net moment of ∼3.7μ(B). Both Co- and Ni-containing phases exhibit spin glass behavior at T(G) = 23 and 30 K, respectively, which is supported by neutron diffraction and a.c. susceptibility data. The structure and physical properties of these four new rhenium based ordered double perovskites are compared to the closely related "pillared perovskites", La(5)Re(3)MO(16), the isoelectronic Os(6+) (5d(2)) double perovskite Sr(2)CoOsO(6), and the Re(6+) (5d(1)) double perovskites, Sr(2)MReO(6), (M = Mg, Ca, Mn, Co, Ni).

ChemInform Abstract: Structural and Magnetic Characterization of the Novel Spin Frustrated Double Perovskite Sr2ScMoO6.

AbstractThe title compound is prepared by solid state reaction of a stoichiometric mixture of MoO3, SrCO3, and Sc2O3.

Monoclinic distortion and magnetic coupling in the double perovskite Sr2−xCaxYRuO6

Abstracts This work investigates in the insulating double perovskites Sr 2− x Ca x YRuO 6 . We address the angular dependence of the strength of the magnetic coupling due to the deviation from planarity of the basal layers of the monoclinic structure, characterized by the in-plane angle α α =144° for x =1) while the bond distances vary in a complex way as a consequence of the strong monoclinic distortion. We found that the magnetic transition temperature, T M , shows a linear dependence on cos [( π − α )/2]. This result is discussed in terms of t 2 g ( π )– e g ( σ ) mixing of the magnetic orbitals of the Ru 5+ ions and unbalanced competitive super-exchange interactions. The deleterious effect of Ca doping for the magnetic coupling is confirmed by the reduction in the short-range antiferromagnetic correlations characteristic of the parent compound at T >> T M and the enhancement of magnetic frustration for T T M .

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.

Rock salt ordered-type double perovskite anode materials for solid oxide fuel cells

B-site rock salt-type ordered double perovskites Sr2 − xBaxMMoO6 − δ (M = Co, Ni; x = 0, 0.5, 1, 1.5 and 2) were evaluated as novel anode materials for SOFC fuel cells. Phase composition, crystal structure, oxygen content, transport properties, chemical stability in relation to ceria electrolyte and chemical stability of Sr2 − xBaxMMoO6 − δ under reducing atmospheres were studied. It was found that Sr2CoMoO6 − δ and Sr2NiMoO6 − δ possess I4/m symmetry at room temperature, while all other anode materials are cubic with Fm-3m space group. SrBaMMoO6 − δ oxides exhibit thermal expansion coefficient in the range 11.7–14.3 · 10− 6 K− 1, which is comparable to that of Ce0.8Gd0.2O1.9 electrolyte. All Sr2 − xBaxMMoO6 − δ oxides show low electrical conductivity in air (ca. 10− 3–10− 1 S cm− 1 at 800 °C). Stability studies performed in reducing conditions indicate that these materials decompose at temperatures lower than 800 °C in 5 vol.% H2 in Ar and lower than 700 °C in pure H2, which suggests that previous literature data showing enhanced conductivity in reducing conditions may not be entirely correct. Interestingly, despite total decomposition of the anode material, relatively high performance of constructed SOFCs was recorded. Moreover, addition of Ni to the anode caused an increase of power density up to 0.16 W cm− 2 at 850 °C.

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.

Raman scattering in the magnetically frustrated double perovskite Sr2YRuO6

The spin correlations and excitations of the Sr2YRuO6 double perovskite are investigated by means of Raman scattering, complemented by synchrotron X‐ray diffraction measurements. Anomalous softening of a breathing mode of the oxygen octahedra is observed below ~200 K, much above the long‐range antiferromagnetic ordering temperature, TN1 = 32 K, due to a spin‐phonon coupling mechanism in the presence of magnetic correlations. A diffusive Raman signal is also observed, possibly associated with spin excitations within magnetically correlated regions. Our results point to a characteristic energy and temperature scale of ~25 meV/200 K below which unusual behavior associated with magnetic correlations is observed in this material. Copyright © 2013 John Wiley &amp; Sons, Ltd.

The structural and electrical properties of Sr2Ni0.75Mg0.25MoO6 and its compatibility with solid state electrolytes

The double perovskite Sr 2 Ni 0.75 Mg 0.25 MoO 6 was evaluated as a potential anode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). Its phase stability, electrical conductivity, thermal and chemical compatibility with perspective oxygen-ionic (Zr 0.85 Y 0.15 O 2 − δ , Ce 0.8 Sm 0.2 O 2–δ , La 0.88 Sr 0.12 Ga 0.82 Mg 0.18 O 3 − δ ) and protonic (BaCe 0.8 Sm 0.2 O 3 − δ , Ba 2 In 1.67 W 0.33 O 5 + δ ) electrolytes were investigated. The Sr 2 Ni 0.75 Mg 0.25 MoO 6 sample was obtained via the combustion method at 1373 K in air. X-ray powder diffraction data and dilatometric measurement show that there is a tetragonal → cubic structure phase transition at 510 K. It was found that the total electrical conductivity of a molybdate ceramic sample strongly depends on the ambient atmosphere and changes from 0.007 S/cm (pO 2 = 0.21 atm) to 33.217 S/cm (pO 2 = 1 × 10 − 19 atm) at 1073 K, respectively. By dilatometry measurement under isothermal conditions it was established that the rapid change in conductivity is most probably connected to the partial reduction of the Mo-ions. TEC values calculated in two temperature ranges of 300–500 K and 500-1073 K were 12.3 × 10 − 6 and 13.5 × 10 − 6 K − 1 , respectively. • Sr 2 Ni 0.75 Mg 0.25 MoO 6 was synthesized and evaluated as anode materials for IT-SOFCs. • The material is redox stable. • Electrical conductivity of Sr 2 Ni 0.75 Mg 0.25 MoO 6 reaches 33.37 S·cm − 1 at 1073 K (pO 2 = 1·10 − 18 atm). • The material is chemically and thermally compatible with some IT-SOFC electrolytes.

Theoretical prediction of half-metallic materials in double perovskites Sr2Cr(Co)B′O6 (B′=Y, La, Zr, and Hf) and Sr2V(Fe)B′O6 (B′=Zr and Hf)

Abstract In this work, we have investigated stable half-metallic materials of the double perovskites Sr 2 BB′ O 6: Sr 2 Cr(Co) B′ O 6 ( B′ = Y, La, Zr and Hf) and Sr 2 V(Fe) B′ O 6 ( B′ = Zr and Hf). Based on the density functional theory, the calculations are conducted with full structural optimization. Generalized gradient approximation (GGA) and additional correlation effect (GGA+ U ) are used. In the GGA+ U scheme, the energy gaps of Sr 2 CoZrO 6 are opened in both spin-channels and become ferromagnetic insulators (FM-Is); Sr 2 CoZrO 6 , Sr 2 CoHfO 6 , Sr 2 FeZrO 6 , and Sr 2 FeHfO 6 transfer from low-spin state to high-spin state. The half metallicity are attributed by the double-exchange interaction mechanism via the B ( t 2g )–O(2 p )– B’ ( t 2g ) π-bounding.