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FTIR transmittance spectra of the Ba2−xSrxZnWO6 (x = 1, 1.25, 1.50, 1.75, 2) double perovskite series.
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Ba2−xSrxZnWO6 double perovskite (DP) oxide compounds (x = 1, 1.25, 1.5, 1.75, 2) were successfully created by means of conventional solid-state techniques. The crystal structures of our series were studied using an X-ray diffractometer. The x = 1 compound has a cubic (Fm-3m) crystal structure, the 1 ≤ x ≤ 2 compounds have tetragonal (I4/m) symmetry...
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... stretching vibration of the WO6 octahedron appears as a high-intensity band around 825 cm −1 . As shown in Figure 6, which shows the transmittance of the series versus the wave number, all samples were confirmed to have molecular bands corresponding to the perovskite oxide form [34]. Raman spectra of the studied samples can be observed in Figure 7. The Raman mode of the Ba2−xSrxZnWO6 samples are classified into two types of lattice vibrations: a bending vibration mode (W-O-W) in the 200-500 cm −1 range and a stretching mode (W-O) in the middle of the 700-950 cm −1 range [35,36]. ...
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... The former technique was recorded on a single crystalline grain, hoping to minimize large peak widths. After meticulous deconvolution, increasing the number of visible modes from 12 to 18, the specific peak positions were analyzed with regard to literature-based mode assignments of other, isostructural compounds summarized in Table 5. 30,[88][89][90][91][92] As can be seen, the number of detected Raman peaks exceeds the twelve modes predicted by group theory for perfect I2/m (7A1g+5Bg) as well as R-3 (4Ag+4 1 Eg+4 2 Eg) space groups (for the total number of predicted phonon modes and their irreducible representations see Table S2). This may be due to different Pr 3+/4+ /W 4+,5+ ion pairing, and the presence of interstitial defects and vacancies. ...
We report details on the synthesis and properties of barium praseodymium tungstate, Ba2PrWO6, a double perovskite that has not been synthesized before. Room-temperature (RT) powder X-ray diffraction identified the most probable space group (SG) as monoclinic I2/m, but it was only slightly distorted from the cubic structure. X-ray photoelectron spectroscopy confirmed that the initial (postsynthesis) material contained praseodymium in both 3+ and 4+ charge states. The former (Pr3+) disappeared after exposure to UV light at RT. Photoluminescence studies of Pr3+ revealed that Ba2PrWO6 is an insulator with a band gap exceeding 4.93 eV. Pressure-dependent Raman spectroscopy excluded the possibility of a phase transition up to 20 GPa; however, measurements between 8 and 873 K signified that there might be a change toward the lower symmetry SG below 200 K. Electron paramagnetic resonance spectra revealed the presence of interstitial oxygen which acts as a deep electron trap.
... The type of crystal symmetry changes depending on t G . From literature, it is known that the crystal symmetry is orthorhombic for 0.97 > t G [47,48]. According to the calculated t G value, the samples synthesized in this study were crystalized in orthorhombic symmetry. ...
... 48 It is well known that the stability of these structures is sensitive to different effects such as temperature, pressure, and identities of A and B cations. [49][50][51][52][53][54][55][56][57][58] Depending on temperature, e.g., Sr 2 MnTeO 6 undergoes two phase transitions according to the sequence P2 1 /n → I4/m → Fm3m. 59 At high temperatures, the two double perovskites SrCaCoTeO 6 and SrCaNiTeO 6 show a phase transition sequence of P2 1 /n (a − a − c + ) → I2/m (a − a − c 0 ) → I4/m (a 0 a 0 c − ) → Fm3m (a 0 a 0 a 0 ). ...
... This diversity in the size occurs during the preparation of the samples (because of high-temperature calcination) and some very small particles appear through grinding the samples. 51 Besides, the boundaries of the particles are easily observed from these SEM images. Fig. S4 in the ESI † shows the energy-dispersive X-ray (EDX) spectra of the series. ...
Polycrystalline double perovskite-type Sr2(Co1-xFex)TeO6 with various stoichiometric compositions (x = 0, 0.25, 0.5, 0.75, and 1) were synthesized by solid-state reactions in air. The crystal structures and phase transitions of this series at different temperature intervals were determined by X-ray powder diffraction, and from the obtained data the crystal structures were refined. It has been proven that for the compositions x = 0.25, 0.50, and 0.75, the phases crystallize at room temperature in the monoclinic space group I2/m. Down to 100 K, depending on the composition, these structures experience a phase transition from I2/m to P21/n. At high temperatures up to 1100 K their crystal structures show two further phase transitions. The first one is a first-order phase transition, from monoclinic I2/m to tetragonal I4/m, followed by a second-order phase transition to cubic Fm3̄m. Therefore, the phase transition sequence of this series detected at temperatures ranging from 100 K to 1100 K is P21/n → I2/m → I4/m → Fm3̄m. The temperature-dependent vibrational features of the octahedral sites were investigated by Raman spectroscopy, which furthermore complements the XRD results. A decrease in the phase-transition temperature with increasing iron content has been observed for these compounds. This fact is explained by the progressive diminishing of the distortion of the double-perovskite structure in this series. Using room-temperature Mössbauer spectroscopy, the presence of two iron sites is confirmed. The two different transition metal cations Co and Fe at the B sites allow exploring their effect on the optical band-gap.
... Studies on double perovskite compounds have attracted huge attention of numerous researchers due to its diversity of structural, magnetic and electrical properties [1][2][3] . Due to the existence of these characteristics, double perovskites are widely sought-after in the development of a variety of applications, such as low field magneto resistive sensors, magnetic random access memories (MRAM) 4 , microwave devices 5 and solar cells 6 . Generally, double perovskites which are derived from conventional perovskites, ABO 3 7 have a general formula AA'BB'O 6 or A 2 BB'O 6 where A is categorized as alkaline earth metals such as Sr, Ca and Ba, B = Fe, Co, Ni, Cr and B' = Mo, W, Re, U are transition metal ions. ...
... Due to the existence of these characteristics, double perovskites are widely sought-after in the development of a variety of applications, such as low field magneto resistive sensors, magnetic random access memories (MRAM) 4 , microwave devices 5 and solar cells 6 . Generally, double perovskites which are derived from conventional perovskites, ABO 3 7 have a general formula AA'BB'O 6 or A 2 BB'O 6 where A is categorized as alkaline earth metals such as Sr, Ca and Ba, B = Fe, Co, Ni, Cr and B' = Mo, W, Re, U are transition metal ions. In these compounds, A site cations are the largest atom compared to B site cations which are 12-fold coordinated meanwhile B and B' cations are six-fold coordinated to the oxygen. ...
... However, gradually increasing the size of the A site cation by substituting the alkaline earth cation of Sr 2+ with Ba 2+ resulting in a structural phase transition from tetragonal to cubic 10 www.nature.com/scientificreports/ (Fm3 m) to monoclinic (P21/n) phase when Sr 2+ was doped at the A site in Ba 2-x Sr x ZnWO 6 (1.00 ≤ x ≤ 2.00) 6 . Apart from that, it was reported in a different study that Ca 2 NiWO 6 had a monoclinic structure with the space group P21/n 11 . ...
In this paper, Sr2–xCaxNiWO6 (x = 0.00, 0.02, 0.04, 0.06) were synthesized using a solid-state reaction method. The crystal structure, optical and dielectric properties of the compounds were examined using X-ray diffraction (XRD), scanning electron microscope (SEM) with energy dispersive (EDX) analysis, Ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy and electrochemical impedance spectroscopy respectively. The Rietveld refinement of XRD confirmed that the compounds crystallized in a tetragonal structure with a space group I4/m. According to the SEM images, the grain sizes of the compounds decreased as the dopant increased. The UV–vis analysis revealed that the band gap energy of the compounds decreased from 3.17 eV to 3.13 eV as the amount of doping increased from x = 0.00 to x = 0.06. A dielectric characterization showed that the dielectric constant (ε′) and dielectric loss (tan δ) for all compounds possessed a similar trend where it was higher in low-frequency area (~ 1 Hz) and dropped instantaneously with the enhancement of frequency up to 1 MHz until it reached constant values.
... As per the literature, the tolerance factor for tetragonal symmetry should lie between 0.974 and 0.993. 20 Since our calculated value falls well within the reported range, hence we may estimate that our composite has crystallized in the tetragonal phase. Together with the information on the best possible lattice structure, the POWD refinement outcomes also include information regarding the lattice parameters. ...
The multiferroic nature of the Mg2FeNbO6 complex oxide ceramic, prepared by a mixed oxide reaction route is presented. A phase transformation to the tetragonal symmetry was identified from refinement analysis. The optical band gap was estimated to be 1.58 eV with the direct allowed transition consideration. From the temperature-dependent dielectric parameter study, magnetic phase transitions at various Tc values were seen, together with some glassy dynamics. The CIS spectroscopy revealed the dominance of grains toward the complex impedance response of the composite. The conductivity of the compound was found to be following Jonscher’s universal power quite ideally. The plot of μB/unit mass versus manifests itself as a weak but well-saturated magnetic ordering in the ceramic, with a low retentivity value of 0.0286 emu/gm. The multiferroic nature of the oxide material is confirmed by the existence of a room temperature (P-E) hysteresis loop, with remnant polarization of Pr=1.2 µC/Cm2.
... The stability and eventual distortion of the structure can be evaluated using Goldschmidt's tolerance factor, which is useful in evaluating the types of oxides in the A 2−x A x BB O 6 double perovskite series [20,21]: ...
... Depending on the value of t, the crystal structure may be diverse: for t > 1.05, the structure is hexagonal; for 1.05 > t > 1.00, it is cubic (Fm-3m); for 1.00 > t > 0.97, it is tetragonal (I4/m); and for t < 0.97, it is monoclinic (P21/n) or orthorhombic [21]. ...
... Several technologies are used for the synthesis of double perovskite structures as particles, in bulk, or as thin films (solid-state reaction, coprecipitation, pulsed laser deposition, rf sputtering, etc.) [17][18][19][20][21][22][23][24][25]. ...
Highly transparent thin films with the chemical formula BaSrMgWO6 were deposited by spin coating using a solution of nitrates of Ba, Sr, and Mg and ammonium paratungstate in dimethylformamide with a Ba:Sr:Mg:W ratio = 1:1:1:1. XRD, SEM, EDX, and XPS investigations evidenced that annealing at 800 °C for 1 h results in an amorphous structure having a precipitate on its surface, and that supplementary annealing at 850 °C for 45 min forms a nanocrystalline structure and dissolves a portion of the precipitates. A textured double perovskite cubic structure (61.9%) was found, decorated with tetragonal and cubic impurity phases (12.7%), such as BaO2, SrO2, and MgO, and an under-stoichiometric phase (24.4%) with the chemical formula Ba2−(x+y) SrxMgyWO5. From transmittance measurements, the values of the optical band gap were estimated for the amorphous (Egdir = 5.21 eV, Egind = 3.85 eV) and nanocrystalline (Egdir = 4.69 eV, Egind = 3.77 eV) phases. The presence of a lattice disorder was indicated by the high Urbach energy values and weak absorption tail energies. A decrease in their values was observed and attributed to the crystallization process, lattice strain diminution, and cation redistribution.
... where hn is the incident photon energy, E g represents the band gap energy and n is the constant values of 0.5, 2, 1.5 and 3 for direct allowed, indirect allowed, direct forbidden and indirect forbidden transition, respectively. 6,24,25 This plot shows that the value of n is 0.5, and the curve has a linear part of. Therefore, the compounds are classied as direct band gap semiconductor, whose top of the valence band and bottom of the conduction band occur at the same value of momentum. ...
... The intensity of peaks increases as the Zn content increases. A strong absorption band at 300 nm to 450 nm may be related to the charge transfer transition between doped Zn 2+ and O 2À (valence and conduction band) in the lattice structure.18,24 As Zn 2+ increases, the increase of reectance value of compound shows the reduction of absorbance properties. ...
In this paper, Sr2Ni1-xZnxTeO6 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) double perovskite compounds were synthesised by the conventional solid-state method, and the structural, optical and dielectric properties were investigated. The Rietveld refinement of X-ray diffraction data shows that all compounds were crystallised in monoclinic symmetry with the I2/m space group. Morphological scanning electron microscopy reported that the grain sizes decreased as the dopant increased. The UV-vis diffuse reflectance spectroscopy conducted for all samples found that the optical band gap energy, Eg, increased from 3.71 eV to 4.14 eV. The dielectric permittivity ϵ′ values increased for the highest Zn-doped composition, Sr2Ni0.2Zn0.8TeO6, being ∼1000 and ∼60 in the low- and high-frequency range, respectively. All samples exhibited low dielectric loss (tan δ ≤ 0.20) in the range of 104-105 Hz frequency. Impedance measurement revealed that grain resistance decreased with enhancement in Zn content in the Sr2NiTeO6 crystal lattice.
... One class of perovskites are double perovskites with the general formula of A 2−x A x 'BB'O 6 , where alkaline metals or lanthanides usually occupy A and A' sites while B and B' positions are reserved for transition metal ions. Double perovskites mostly crystallize in a rock salt cubic crystal structure, but the tetragonal, orthorhombic, and monoclinic one is also possible [2,5,10,11]. The structure of the perovskite compound can be evaluated using Goldschmidt's tolerance factor (t). ...
Four tungstate double-perovskite materials with a general formula A2BWO6, where A=Ba, Sr and B=Mg, Zn were synthesized by co-precipitation method. All samples exhibit blue emission under UV excitation resulting from the additional electron states within the material’s band gap created by two types of centers: the regular and the inversion tungstate groups. The latter one is defined as a W⁶⁺ ion residing at the octahedral B site (B = Mg, Zn). The relative position of those two centers’ energy levels to the valence and conduction bands can be altered by the substitution to the A site (Ba/Sr) as well as the B site (Mg/Zn). Substitution of Sr for Ba results in a blue-shift of both excitation and emission spectrum. The substitution of Zn for Mg, in contrast, results in the opposite phenomenon. The substitutions, aside from shifting the emission wavelength of the centers, regulate the ratio between regular and inversion tungstate groups by restricting or allowing the energy transfer between them and influence their thermal stability. The luminescence properties are in agreement with the DFT calculations. The ability to influence their host emission wavelength, intensity, and thermal stability can be crucial in the design of novel luminescent thermometers.
