The growing demand for sustainable energy has intensified the search for efficient photovoltaic materials with suitable bandgaps. Multiferroic oxides (M3TeO6) have emerged as promising candidates for solar-energy harvesting due to their structural flexibility and strong electron-lattice coupling. However, a unified physical understanding of their pressure-dependent bandgap evolution, particularly the role of Jahn-Teller effects (JTE), remains elusive. In this work, we investigate the structural and electronic evolution of Cu3TeO6 as a function of pressure using synchrotron-based X-ray diffraction (XRD), Raman spectroscopy, and UV-vis absorption techniques. We discovered a complicated bandgap response of Cu3TeO6, characterized by an initial widening followed by a sharp collapse, corresponding to the sequential phase transitions Ia3¯ → Ibca → P2/m. The low-bandgap state of Cu3TeO6 (∼2.28 eV) is quenchable to ambient pressure. This bandgap behavior of Cu3TeO6 can be rationalized by the competition between octahedral distortion and bond-length compression. At low pressures, octahedral tilting may reduce effective orbital overlap, widening the bandgap, whereas at high pressures, Cu–O shortening is expected to enhance Cu 3d–O 2p wave-function overlap, triggering the bandgap collapse. By comparing M3TeO6 systems (M = Mn, Co, Cu) with varying Jahn-Teller strengths, we suggest that compression energy is partitioned differently across these materials. In strong-JTE compounds, a significant portion of the applied pressure is consumed in suppressing Jahn-Teller distortions, thereby delaying structural transitions and moderating the rate of bandgap collapse. These findings provide a useful working framework for understanding pressure-dependent bandgap evolution in representative M3TeO6 tellurates and underscore the utility of high pressure as a controllable tool for rational bandgap tuning in multifunctional and correlated oxide materials.

A NASICON-type sodium-ion conducting material was synthesized via the glass-ceramic route by investigating the zinc doped Na2O-Al2O3-TiO2-P2O5 system. The glasses and glass-ceramics corresponding to the formula Na2+xAl1-xZnxTi(PO4)3 (x = 0, 0.2, 0.4, 0.6, 0.8, 1), labeled as (NAZTP-Gx) and (NAZTP-GCx) respectively, were characterized using different techniques. Differential Scanning Calorimetry (DSC) measurements were carried out to identify the characteristic temperatures, the glass transition (Tg) and the crystallization temperature (Tc). X-ray Diffraction (XRD) analysis of the glass-ceramics confirmed the formation of a solid solution Na2+xAl1xZnxTi(PO4)3 NASICON phase, Theoretical calculations employing the Perdew-Burke-Ernzerhoff generalized gradients approximation (PBE-GGA) model supported the potential substitution of aluminum by zinc in the octahedral site in the NASICON-phase. Further structural insights were obtained through Infrared (IR) and Raman spectroscopies. Scanning electron microscopy (SEM) analysis revealed a distinct flower-like shape of the formed crystallites in the glass-ceramic NAZTP-GC0.2. Electrical characterization using electrochemical impedance spectroscopy (EIS) demonstrated that the NAZTP-GC0.2 sample exhibited the highest ionic conductivity at 300 degrees C, reaching 4.1 x 10-5 (Omega- 1 cm- 1) with an activation energy of 0.25 eV. The DC polarization was performed on the NAZTP-GC0.2 glass-ceramic, revealing that the ions are the main charge carriers in the sample. This comprehensive analysis provides valuable insights into the partial zinc doping of NASICON glass-ceramics, offering potential for improved performance as solid electrolytes in various applications.

Double perovskites represent a class of materials with promising fundamental properties and a broad spectrum of potential applications. However, the wide bandgap energy in double perovskites presents a hindrance to further enhancement of their photovoltaic efficiency. In the present study, a high-pressure technique is employed to tune the bandgap energy of double perovskite Co3TeO6 (CTO). A giant bandgap reduction of ∼37% from 2.93 to 1.85 eV has been observed after high-pressure treatment. Subsequent synchrotron-based X-ray diffraction and Raman spectroscopy results reveal that the significant bandgap reduction of CTO accompanies a sequence of structural phase transitions during compression and decompression. Furthermore, the high-pressure phase with a smaller bandgap energy of 1.85 eV turns out to be quenchable to ambient conditions, making the quenched CTO a promising light-harvesting material for photovoltaic applications. The present results demonstrate that high pressure can represent a green and efficient technique to tune the properties of multifunctional materials and serve as a guide for searching for stable and environmentally friendly light-harvesting materials.

Spinels represent a class of ceramics with promising fundamental properties and a broad spectrum of industrial applications. However, the knowledge of pressure effects on the crystal structure of spinel is limited, which hinders their efficient synthesis using high-pressure techniques. In this paper, the effect of pressure on the crystal structure of mixed spinel ferrite Fe0.8Ni1.8Sb0.4O4 was investigated at room temperature by in situ synchrotronbased X-ray diffraction and Raman spectroscopy up to 42.19 GPa and 49.51 GPa, respectively. The X-ray diffraction results indicate that Fe0.8Ni1.8Sb0.4O4 adopts the cubic (spinel-type, space group Fd (3) over barm) structure at ambient conditions, which undergoes a pressure-induced structural transition to a monoclinic phase (space group P2(1)/c), commencing at 20.83 GPa. This sluggish structural transformation turns out to be of the first-order accompanied by a volume collapse of about similar to 2.2 % when completed at 29.68 GPa. A second phase transition to yet another metastable monoclinic structure with space group C2/m is observed to begin at 33.56 GPa. However, this phase transition does not complete even up to the highest pressure applied in the study. Raman results confirm that Fe0.8Ni1.8Sb0.4O4 undergoes a pressure-induced phase transition from Fd (3) over barm to P2(1)/c at 27.34 GPa. The observed phase transitions are reversible, and their mechanisms are discussed in the light of the Raman spectroscopy data. The present study deepens our understanding of the high-pressure behavior of spinels, which will facilitate their industrial syntheses and a better understanding of their role in planetary interiors.

Advancing energy density, enabling lithium metal anodes, and ensuring unparalleled safety and operational reliability in lithium batteries hinge on advancing inorganic solid-state electrolytes. To overcome current impediments, we present an innovative approach that integrates glass-ceramics with a pioneering new Nasicon strategy involving molybdenum doping. In the conducted study, a series of 14Li2O-9Al2O3-38TiO2-(39-x)P2O5-xMoO3 glasses, denoted as LATPMox, along with their corresponding glass-ceramics (LATPMox-GC), have exhibited a promising characteristic as solid electrolytes. X-ray diffraction (XRD) analysis confirms the formation of the novel Mo-doped Nasicon phases in the glass-ceramics, as validated by Rietveld refinement. Examination of the crystallization kinetic behavior of the glasses reveals a three-dimensional nucleation process with spherical particle growth, featuring an activation energy of 165 kJ.mol-1. Transmission Electron Microscopy TEM characterization aligns crystallization behavior with crystallite and distribution within the glass matrix, resulting in a compact and dense microstructure. The structural properties of the resultant phases are examined through FT-IR, Raman spectroscopy, and TEM-SEAD analysis. Vickers indentation tests were employed to assess the microscopic fracture toughness, and both the glass and glass-ceramics materials demonstrated favorable mechanical performance. Optical characterization using UV-visible absorption highlights the reduction of Mo6+ to Mo5+, likely occupying tetrahedral sites within the crystalline lattice. Impedance spectroscopy measurement showcases the effective promotion of ionic conductivity following Mo doping, reaching a total conductivity value of 5.50×10-5 Ω-1.cm-1 along with a high lithium transference number of 0.99 at room temperature for LATPMo2.6-GC glass-ceramic. This value is larger than that of many other glass-ceramics as well as that of the well-known lithium phosphorous oxy-nitride LiPON solid electrolyte whose ionic conductivity at RT is around 2×10-6 Ω-1.cm-1.

Advancing energy density, enabling lithium metal anodes, and ensuring unparalleled safety and operational reliability in lithium batteries hinge on advancing inorganic solid-state electrolytes. To overcome current impediments, we present an innovative approach that integrates glass-ceramics with a pioneering new Nasicon strategy involving molybdenum doping. In the conducted study, a series of 14Li2O-9Al2O3-38TiO2-(39-x)P2O5xMoO3 glasses, denoted as LATPMox, along with their corresponding glass-ceramics (LATPMox-GC), have exhibited a promising characteristic as solid electrolytes. X-ray diffraction (XRD) analysis confirms the formation of the novel Mo-doped Nasicon phases in the glass-ceramics, as validated by Rietveld refinement. Examination of the crystallization kinetic behavior of the glasses reveals a three-dimensional nucleation process with spherical particle growth, featuring an activation energy of 165 kJ mol-1. Transmission Electron Microscopy TEM characterization aligns crystallization behavior with crystallite and distribution within the glass matrix, resulting in a compact and dense microstructure. The structural properties of the resultant phases are examined through FT-IR, Raman spectroscopy, and TEM-SEAD analysis. Vickers indentation tests were employed to assess the microscopic fracture toughness, and both the glass and glass-ceramics materials demonstrated favorable mechanical performance. Optical characterization using UV-visible absorption highlights the reduction of Mo6+ to Mo5+, likely occupying tetrahedral sites within the crystalline lattice. Impedance spectroscopy measurement showcases the effective promotion of ionic conductivity following Mo doping, reaching a total conductivity value of 5.50 x 10-5 Omega- 1 cm- 1 along with a high lithium transference number of 0.99 at room temperature for LATPMo2.6-GC glass-ceramic. This value is larger than that of many other glass-ceramics as well as that of the well-known lithium phosphorous oxy-nitride LiPON solid electrolyte whose ionic conductivity at RT is around 2 x 10-6

The multiferroic material Pb3Mn7O15 3 Mn 7 O 15 exhibits a high resistivity arising from the orbital electrons localized around the manganese ions, which hinders its potential applications. Previous studies indicated that the resistivity of Pb3Mn7O15 3 Mn 7 O 15 was influenced by its crystal structure and the distribution of Mn ions. Consequently, pressure-induced structural change are expected to represent a viable method for tuning the resistivity and other properties of this compound. In the present study, the pressure effect on the resistivity of Pb3Mn7O15 3 Mn 7 O 15 was investigated up to 42 GPa. Furthermore, the X-ray diffraction and Raman spectroscopy techniques, along with the density functional theory calculations were employed to study the crystal structure evolution of Pb3Mn7O15 3 Mn 7 O 15 under pressure. The results demonstrate an electronic semiconductor-metal phase transition in Pb3Mn7O15, 3 Mn 7 O 15 , accompanying an irreversible orthorhombic to monoclinic phase transition. Additionally, within the orthorhombic phase, an iso-structural phase transition is observed, originating from the magnetic moments collapse of manganese cations. This study provides compelling evidence that high-pressure processing can be employed to modulate the crystal structure and functional properties of multifunctional materials.

Due to their large bandgaps, multiferroic oxides, the promising candidates for overcoming the disadvantages of metal-halide perovskites as light absorbers, have so far very limited use in solar cell applications. Previous investigations demonstrate that high pressure represents an efficient tool for tuning the bandgap of multiferroic Mn3TeO6 (MTO). However, the underlying mechanism of the giant bandgap reduction discovered in MTO remains unclear, which critically prevents the design of next-generation light absorbers. In this study, we performed in situ x-ray diffraction analyses on the structure evolution of MTO upon compression and decompression, discovering a sequence of irreversible phase transitions R3¯→C2/c→P21/n. The experimental results, supported by electronic structure calculations, show the shortening of Mn–O–Mn bonding, and, to a lower extent, the decrease in connectivity of octahedra across the phase transition, explain the giant bandgap reduction of MTO. These findings will facilitate the design and synthesis of next-generation light absorbers in solar cells.

Glass formation and properties of manganese phosphate glasses containing both Na2O and K2O oxides with the general formula 49.95[xNa(2)O-(1-x)K2O]-0.1MnO(2)-49.95P(2)O(5) with x = 0-1 mol%, have been investigated. The vitreous samples were prepared by standard melt quenching. To get an insight into their physical properties, the density and the glass transition temperature were procedure determined. The structure of the glass was performed by Infrared, Raman, and electron spin resonance (EPR) spectroscopies. The results obtained by these techniques have allowed us to explain their structure and properties upon the variation of the chemical composition. The variation of the glass transition temperature as a function of the composition presents a minimum for the ratio Na/Na + K = 0.5. Infrared and Raman spectroscopies has identified the presence of different structural grouping units in the glassy-network. It is found that the stretching vibration nu(s)(PO2) and nu(s)(P-O-P) are more sensitive to the substitution of alkali elements. EPR experiments have shown the presence of Mn2+ centers in the glasses. The variation of the g-factor as a function of the composition is non-linear. The non-linearity behavior of the composition dependence of Tg, vibration bending mode, and the g-factor are a fingerprint of the mixed alkali effect in the glasses under study. (C) 2020 Elsevier Ltd. All rights reserved.

A series of double-perovskite oxides Sr2Sr1-xCaxTeO6 (0 ≤ x ≤ 1) samples have been prepared in order to study the effect of composition on phase formation and the related optical properties. The objective of this work is to study the possibility of calcium insertion with different percentages since calcium in known to enhance the electrical properties. In this work a well detailed structure and phase transitions investigation of the compounds were conducted and probed by X-ray diffraction and Raman spectroscopy techniques at room temperature. Both Rietveld refinements and Raman studies revealed that two phase transitions took place as the calcium amount x increases; a first from a triclinic to a hexagonal in the range 0.1 < x < 0.25 and a second from the hexagonal to a monoclinic structure in the range 0.5 < x < 0.6. The optical absorption α(λ) was also determined as a function of calcium content in the series samples using UV-vis analysis. It was revealed that a remarkable change occured in the cut-off wavelength, confirming the sequence of phase transitions C1 → R $$ \overline{3} $$ m → P21/n. The optical band gap measurements showed that the triclinic Sr3TeO6 and the monoclinic Sr2CaTeO6 phases have band gap values of 2.75 and 2.81 eV, respectively. When the calcium increased to x = 0.25 (Sr2.75Ca0.25TeO6), remarkable decrease of the band gap value was observed, with Eg = 2.627 eV.

The main goal of this work is to study the physical, structural, optical, and electrical properties of alkali zinc phosphate glasses doped with CoO oxide with the general formula 10Li2O-xCoO-(40-x)ZnO?50P2O5. Using the standard melt-quench technique, a large glass-forming region is obtained, and up to 40 mol% CoO doped glasses are prepared. XRD diffraction confirmed the amorphous nature of these materials. Density, molar volume, and the glass transition temperature (Tg) are composition-dependent. Infrared (IR) spectroscopy is performed to study the structural approach. It is observed that the substitution of ZnO by CoO oxide in the glassy framework induces some structural modifications. The UV?Visible spectra of the CoO-doped glasses show visible absorption bands in the region 400?700 nm which are related to the coexistence of cobalt in divalent and trivalent states. The crystallization behaviour of the samples is performed by submitting the glasses to controlled heat treatments and the crystalline phases obtained are identified by X-Ray diffraction (XRD). The kinetic of the crystallization is carried out by employing the thermal analysis (DSC) technique. The crystallization process is discussed regarding the obtained activation energy (Ec) and Avrami parameter (n). The Vickers hardness values of the glasses and the glass-ceramics are determined and discussed according to the bond strengths. The electrical conductivity of these materials is investigated over a large frequency domain at various temperatures. It is found that the electric conductivity decreases with increasing cobalt content. It is also noted that the conductivity of each glass-ceramic is reduced in comparison with that of its mother glass. The frequency-dependent of the conductivity follows Jonscher?s power law and the correlated barrier hopping mechanisms (CBH) was appropriate for the conduction process inside the glasses. The electrical modulus formalism is applied to the electric data in order to study their dielectric relaxation. The results show that this latter is non-Debye type in agreement with the well-known universal responses of amorphous materials.

In this study, a new assemblage of Ediacaran metazoan fossils is reported from the basal Stáhpogieddi Formation on the Digermulen Peninsula of Arctic Norway, including Anulitubus n. gen. Moczydłowska in Moczydłowska et al., Anulitubus formosus n. gen. n. sp. Moczydłowska in Moczydłowska et al., Coniculus n. gen. Moczydłowska in Moczydłowska et al., Coniculus elegantis n. gen. n. sp. Moczydłowska in Moczydłowska et al., Fistula n. gen. Moczydłowska in Moczydłowska et al., and Fistula crenulata n. gen. n. sp. Moczydłowska in Moczydłowska et al. The specimens are three-dimensionally preserved and include tubular and conical skeletons that are morphologically distinguished by their body-wall constructions, radial symmetry, polarity, segmentation, and annulation. The skeletons are interpreted to be biomineralized by primary silica based on computed micro-tomographic, petrographic, geochemical, and spectroscopic evidence of originally rigid body wall with layers of constant thicknesses, composed of opal, microcrystalline quartz, and an admixture of carbonaceous material, which differ from the host sediment mineralogy and do not show replacement or encrustation. The fossil-bearing interval immediately overlies strata of Gaskiers age and can be bracketed within 580–541 Ma, but it is estimated to be ca. 575 Ma on the basis of averaged sedimentation rates and biostratigraphic correlations with Ediacaran biota found in up-section deposits of ca. 558–555 Ma. Future new findings of such fossils in different preservation modes and further multi-collector inductively coupled plasma mass spectrometry, which shows the silicon fractionation and traces its biogenic origin versus inorganic mineralization, may corroborate the interpretation of biogenic silicification of these earliest skeletal fossils. UUID: https://zoobank.org/6bccada1-870e-47b0-b819-82685152ea54

Polycrystalline samples of the series of triple perovskites Sr3−xPbxFe2TeO9 (0 ≤ x ≤ 2.25) (SPFTO) were synthesized using solid state reaction. These materials have been studied by a combination of X-ray powder diffraction (XRPD), Mössbauer spectrometry, Raman and UV–Vis spectroscopies. The crystal structures were resolved by the Rietveld refinement method, and revealed that this Sr3−xPbxFe2TeO9 (0 ≤ x ≤ 2.25) system shows one space group change from tetragonal I4/m (0 ≤ x ≤ 1) to another tetragonal form I4/mmm (1.25 ≤ x ≤ 1.88) and a second transition to hexagonal $$R{\overline{3}}m$$ (2.08 ≤ x ≤ 2.25). An anti-site disordering of Fe and Te on the B sites has been detected indicating the presence of a partial amount of Te at Fe positions and vice versa. The valence state of iron in the Fe site was determined to be Fe(III) by Mössbauer spectrometry, which also revealed two sites in a concordance with the XRPD measurements. 57Fe Mössbauer spectra measurements show paramagnetic and magnetic ordering behaviors. The observed Raman spectra as a function of composition show obvious changes on the positions (wavenumbers), the FWHM and the intensities of the modes confirming the phase transformations observed by the XRPD results. These structural transitions led to a distinct change in the optical band gap energy, varying from 2.14 to 1.85 eV.

Glasses in the system (1 − x)(0.5NaPO3–0.5KPO3)–xMnO2, with 0 ≤ x ≤ 50 mol%, have been prepared using a melt-quench route. The glasses exhibit a yellow to dark color with the increase in manganese content owing to the presence of Mn2+ and Mn3+ ions in the network. The amorphous state of the glasses is evidenced by the X-ray diffraction. In order to get an insight into the physical and structural aspects of these vitreous materials, we have determined some of their parameters such as density, molar volume and glass transition temperature. From differential thermal analysis scan on heating, we evaluated the glass transition temperature (Tg) of each glass, which corresponds to the phase transition temperature from solid to viscous liquid. The density (ρ) as a structural index is found to increase while the corresponding molar volume decreases with MnO2 content. The structural approach of the studied glasses is evaluated by infrared (IR) and electron paramagnetic resonance (EPR) spectroscopies. IR technique allowed us to identify the coexisting bond vibration modes in the glass network, and it has shown that many structural phosphates units coexist, mainly pyrophosphate and metaphosphate structural groups. EPR experiments have shown the presence of Mn2+ centers in the glasses. The UV–Visible absorption is utilized to estimate the values of the optical band gap (Eg) and Urbach energy (ΔE). The optical band gap energy is determined from both the absorption spectrum fitting (ASF) and Tauc’s methods. These optical parameters are composition dependence. The dc conductivity of the glasses is determined in the temperature range from 303 to 473 K. It decreases with increasing manganese content. It is thermally activated and followed an Arrhenius behavior. The crystallization of glasses is realized by submitting them to heat treatments, and the crystallized phases are identified by XRD analysis. The crystallization kinetic was studied under non-isothermal conditions. The activation energy (Ec) and the Avrami parameter (n) were determined.

Sr 1.50 Ca 1.50 Fe 2.25 Mo 0.75 O 9−δ and Sr 1.92 Ca 1.08 Fe 1.04 W 0.96 O 9−δ double perovskites are synthesized in the polycrystalline form by a solid-state reaction route in air and studied at room temperature using the of PXRD, Raman and Mössbauer spectroscopy techniques. The Rietveld refinement analysis reveals that both compounds adopt a tetragonal system with the space group I 4/m and lattice parameters a = b = 5.5176(1) Å and c = 7.8065(2) Å for Sr 1.50 Ca 1.50 Fe 2.25 Mo 0.75 O 9−δ and a = b = 5.5453(1) Å and c = 7.8388(1) Å for Sr 1.92 Ca 1.08 Fe 2.04 W 0.96 O 9−δ . Raman spectra are consistent with the group theoretical analysis predicted for tetragonal symmetry I 4/ m (point group C 4 h 5 ). 57 Fe Mössbauer spectra recorded at room temperature show a paramagnetic behavior for Sr 1.50 Ca 1.50 Fe 2.25 Mo 0.75 O 9−δ , and magnetic ordering for Sr 1.92 Ca 1.08 Fe 2.04 W 0.96 O 9−δ . The isomer shift (δ) and quadrupole splitting (Δ) values are characteristic of high-spin Fe 3+ in a distorted octahedral coordination.

The spin state of the Prussian blue analogue FeIIPtIV(CN)6 is investigated in response to temperature, pressure, and X-ray irradiation. While cooling to 10 K maintains the high-spin state of FeII, compression at ambient temperature induces a first-order spin-crossover (SCO) transition with a small hysteresis loop (p↑ = 0.8 GPa, p↓ = 0.6 GPa). In addition, the high-spin to low-spin transition can be initiated at lower pressure through increased X-ray irradiation. Our study highlights a cooperative SCO with moderate pressure in a porous Prussian blue analogue.

Glasses of the composition (50-x/2) K2O-xMnO2-(50-x/2) P2O5 with (0≤x≤30%mol), have been prepared by standard melt quenching procedures. The amorphous state of the glasses is evidenced using the X-Ray diffraction. Their physical properties were characterized by thermal analysis and density measurements. The density and the glass transition temperature increase with increasing in MnO2 content. To study the structural role of MnO2 oxide in studied glasses, the FTIR and Raman spectroscopies have been employed. It was highlighted that the presence of MnO2 allows the depolymerisation of the phosphate chains and formation of covalent bonds P-O-Mn, which replace P-O-P and P=O linkages.

Sr(1.50)Ca(1.50)Fe(2.25)Mo(0.75)O(9-delta)and Sr(1.92)Ca(1.08)Fe(1.04)W(0.96)O(9-delta)double perovskites are synthesized in the polycrystalline form by a solid-state reaction route in air and studied at room temperature using the of PXRD, Raman and Mossbauer spectroscopy techniques. The Rietveld refinement analysis reveals that both compounds adopt a tetragonal system with the space groupI4/m and lattice parametersa=b= 5.5176(1) A andc= 7.8065(2) A for Sr(1.50)Ca(1.50)Fe(2.25)Mo(0.75)O(9-delta)anda=b= 5.5453(1) A andc= 7.8388(1) A for Sr1.92Ca1.08Fe2.04W0.96O9-delta. Raman spectra are consistent with the group theoretical analysis predicted for tetragonal symmetryI4/m(point group C4h5).Fe-57 Mossbauer spectra recorded at room temperature show a paramagnetic behavior for Sr1.50Ca1.50Fe2.25Mo0.75O9-delta, and magnetic ordering for Sr1.92Ca1.08Fe2.04W0.96O9-delta. The isomer shift (delta) and quadrupole splitting (Delta) values are characteristic of high-spin Fe(3+)in a distorted octahedral coordination.

Phosphate glasses are of large interest for a variety of technological applications due to their several unique properties. In this work we investigate structural, optical and electrical properties of some alkali metaphosphate glasses doped with manganese oxide inside the system (50-x/2) K2O-xMnO(2)-(50-x/2) P2O5 with (0 <= x <= 30%mol). The glassy samples have been prepared using a melt-quench process. The obtained glasses are colored and the valence of manganese is composition dependence. The local structure of Mn2+ in the glasses is evaluated by EPR spectroscopy. The optical absorption spectra have been used to evaluate the values of the optical band gap (E-g) and Urbach energy (Delta E). The variation of these optical parameters as a function of composition is investigated. The presence of Mn3+ in the glasses is established by the optical absorption and this ion is associated with the absorption band at 520-530 nm. dc conductivity of the glasses is studied and it is found that it is thermally activated and followed an Arrhenius behavior. (C) 2019 Elsevier Ltd. All rights reserved.

Sr1.50Ca1.50Fe2.25Mo0.75O9–δ and Sr1.92Ca1.08Fe2.04W0.96O9–δ double perovskites are synthesized in the polycrystalline form by a solid-state reaction route in air and studied at room temperature using the of PXRD, Raman and Mössbauer spectroscopy techniques. The Rietveld refinement analysis reveals that both compounds adopt a tetragonal system with the space group I4/m and lattice parameters a = b = 5.5176(1) Å and c = 7.8065(2) Å for Sr1.50Ca1.50Fe2.25Mo0.75O9–δ and a = b = 5.5453(1) Å and c = 7.8388(1) Å for Sr1.92Ca1.08Fe2.04W0.96O9–δ. Raman spectra are consistent with the group theoretical analysis predicted for tetragonal symmetry I4/m (point group C4h5). 57Fe Mössbauer spectra recorded at room temperature show a paramagnetic behavior for Sr1.50Ca1.50Fe2.25Mo0.75O9–δ, and magnetic ordering for Sr1.92Ca1.08Fe2.04W0.96O9–δ. The isomer shift (δ) and quadrupole splitting (Δ) values are characteristic of high-spin Fe3+ in a distorted octahedral coordination.