Half metallic ferroamgnetism,and transport properties of vacancy ordered double perovskites Rb2(Os/Ir)X6 (X = Cl,Br) for spintronic applications

The defected double perovskites, being non-toxic, stable, and capable to exhibit both spin-up (↑) and spin-down (↓) polarizations, are attractive for spintronic devices. In the present article, the role of 5d-electrons of Os and Ir to control the magnetic characteristics of Rb₂(Os/Ir)Cl/Br₆ is addressed. The structural and magnetic characteristics are investigated using PBEsol-mBJ functional, while thermoelectric behaviors are studied using BoltzTrap code. The computed tolerance factors (0.95/0.98, 0.94/0.96) and formation energies (?2.0/-1.65eV, ?1.70/-1.10eV) confirm the structural and thermodynamic stabilities, respectively. The examination of band structures and density of states have revealed half-metallic ferromagnetic nature, which is further discussed in terms of double exchange model, exchange constants and exchange energies. The presented calculations indicate that underlying hybridization process, exchange energy, and crystal field energy induce ferromagnetism due to electron spin. Furthermore, thermal, and electrical conductivities, power factor, and Seebeck coefficients are computed and discussed to understand the thermoelectric applications.     

无铅或少铅钙钛矿CH3NH3M1-xPbxX3(M=Sn,Sr;X=Cl,Br,I)太阳能电池的研究进展

本文综述了Sn2+或Sr2+取代的无铅或少铅钙钛矿CH3NH3PbX3 (X=Cl,Br,I)的结构及其主要的制备方法,评述了各种方法的优缺点.简要介绍了无铅或少铅钙钛矿材料的能隙以及材料的稳定性对太阳能电池的影响,并对其发展前景进行了展望.     

Analysis of optoelectronic and trasnport properties of magnesium based MgSc2X4 (X=S,Se) spinels for solar cell and energy storage device applications

Intense research work is underway for identifying materials with potential applications in energy storage and energy harvesting systems. The magnesium based scandium chalcogenides have recently emerged as potential candidates for Mg batteries owing to their high Mg ionic conductivity and low electron conduction. At the same time, their band gaps are capable of absorbing electromagnetic radiations in visible to UV range; making them suitable for solar cell applications. In order to analyze the application of MgSc₂X₄(X = S, Se) compounds in energy devices, in this work we employ density functional theory calculations using the full potential linear augmented plane-wave method for examining their optoelectronic and thermoelectric properties. For the structural properties, the generalized gradient approximation functional designed for solids (PBEsol-GGA) has been used, while modified Becke and Johnson (mBJ) potential functional is used for computing the optoelectronic and transport properties. Our calculated optical properties indicate that these materials can find applications in solar cells. Moreover, the electronic transport properties computed using Boltzmann transport equation suggest carrier concentrations in MgSc₂S₄ to MgSc₂Se₄ spinels can be tuned for making them suitable for metal ion batteries.     

Spray-deposited kesterite Cu2ZnSnS4 (CZTS): Optical,structural, and electrical investigations for solar cell applications

Kesterite Cu₂ZnSnS₄ (CZTS)-based solar devices have become a popular alternative to copper indium gallium selenide (CIGS) due to its outstanding properties such as high efficiency, non-toxicity, cost-effectiveness, suitable optoelectrical properties, and earth-abundancy. In this study, we directly fabricated CZTS films via a single-step spray pyrolysis technique, in contrast to conventional techniques where post sulfurization is required. The spray deposited CZTS films are investigated for their optical, structural, and electrical properties. The X-ray diffraction (XRD) and Raman analysis study revealed the synthesis of the phase-pure kesterite CZTS films without impurity phases. Large crystallites of CZTS are obtained at a deposition temperature of 400 °C, exhibiting a porous granular morphology with different grain sizes upon temperature variation. The size-dependent optical properties revealed that the CZTS films exhibited admirable visible light absorption of 10⁵ cm^?1 and an electronic bandgap ranging between 1.42 and 1.58 eV. The minimum dielectric loss obtained for optimized CZTS due to fewer intrinsic defects confirmed the materials’ applicability. Thus, the study provides a simple, viable route to fabricate CZTS without post-treatment to build affordable solar cells.     

Influence of the selenization time on the properties of (Na0.1Cu0.9)2ZnSn(S,Se)4 thin films and their photovoltaic solar cells

(Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ thin films with a single kesterite phase were synthesized using a sol-gel spin-coating method accompanied by rapid post-annealing. In this study, we investigated the effect of selenization time on the crystal quality and photoelectric performance of the (Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ films. It was found that the crystallinity and morphology of the films was enhanced, and some of bigger Se substituted for the S site in (Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ with increasing the selenization time. The bandgap of the film can be regulated from 1.04 eV to 0.99 eV by varying the selenization time. In addition, all films showed p-type conductive characteristics, and films with optimal electrical performance could be obtained by optimizing the selenization time. Finally, the (Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ thin film with the best crystal quality and optical-electrical characteristics was obtained at an optimized selenization time of 15 min. A high power conversion efficiency (PCE) of 3.92% was obtained for the (Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ device, which is 42% higher compared to that of the undoped Cu₂ZnSn(S,Se)₄ (CZTSSe) device.     

Crystal structure,phonon modes and dielectric properties of B site ordered ABiLiTeO6 (A = Ba,Sr) double perovskites

ABiLiTeO₆ (A = Ba, Sr) double perovskite oxides were synthesised through conventional solid - state ceramic route. X-Ray diffraction patterns indicated pseudocubic symmetry for both compounds. Deconvoluted Raman spectra using Lorentzian function gave 7 first order Raman modes for both BaBiLiTeO₆ and SrBiLiTeO₆ whereas Infrared spectroscopy gave 8 modes for BaBiLiTeO₆ and 9 modes for SrBiLiTeO₆. Observed phonon modes were in good agreement with the corresponding group theoretical predictions for space group I4/m for both compounds. Rietveld refinement of the XRD patterns also confirmed I4/m space group for ABiLiTeO₆ (A = Ba, Sr) with 1:1 B site ordering of Te⁶⁺ and Li⁺ cations. The random occupancy of Ba²⁺ and Bi³⁺ at the A site in BaBiLiTeO₆ whereas Sr²⁺ and Bi³⁺ in SrBiLiTeO₆ were revealed from Rietveld refinement. Microstructure of both the compounds gave average grain size of less than 3?µm. At 1?MHz, BaBiLiTeO₆ and SrBiLiTeO₆ possess porosity corrected dielectric constants of 49.5 and 34.4 and dielectric losses of 0.029 and 0.028 respectively.     

Comprehensive study of ferromagnetic MgNd2X4 (X = S,Se) spinels for spintronic and solar cells device applications

Full potential LAPW + lo method is used for exploring electronic, structural and thermoelectric properties for MgNd₂X₄ (X = S, Se) spinels that are found to show ferromagnetic-semiconductor behaviour in the spinel structure. The investigated negative value of formation energy and positive value of phonon spectra computed using PBEsol GGA indicates the energetic and dynamical stability of the studied cubic ferromagnetic-semiconductors. We have used TB-mBJ potential functional for electronic and magnetic properties, which lead to a reliable account of electronic structure, demonstrating band occupancy in the spinels along with a clear explanation of density of states. The stability of ferromagnetic state in the studied materials is because of the exchange splitting of Nd cations based on p-d hybridization which is in accordance with the results obtained for electronic band structure and density of states. The exchange splitting of bands can be justified by the spin magnetic moment between anions and cations, and sharing of charge. The computed values of dielectric constant and their associated optical parameters are used to explain the optical active behaviour of the spinels under investigation; indicating that the two spinels studied in the present work are suitable for solar cells device applications. The calculation of thermoelectric properties is very useful for determining a material's potential use in waste energy recovery systems and many other innovative applications.     

Band gap modulation and improved magnetism of double perovskite Sr2KMoO6 (K = Fe,Co, Ni,Mn) doped BaTiO3 ceramics

BaTiO₃ ceramics doped with double perovskite Sr₂KMoO₆ (BT-SKM) are fabricated via solid-state reaction technology. The effects of SKM dopants on the structure, band gap and electrical/magnetic properties of BT are systematically studied. XRD and Raman spectra analysis show polycrystalline perovskite structure of the samples, which confirms the structural changes. With the addition of SKM dopants, the grain size of the samples decreases significantly. The band gaps of doped BT samples reduce, and the minimum band gap of BT-SCM is 1.77 eV, which is apparently reduced compared with the band gap of pure BT of 3.22 eV. However, the ferroelectric properties are weakened in samples doped with SKM. This ascribes to the introduction of more oxygen vacancies by dopants, which impedes the switching of domains, resulting in deterioration of ferroelectric properties. Furthermore, ferromagnetism of BT-SNM is observed, which may be attributed to the long-range exchange interaction between Ni²⁺ ions and oxygen vacancies. These results reveal the potential applications of these perovskite oxides in photovoltaic and memory devices.     

Physicochemical properties of rock salt-type ordered Sr2MMoO6 (M = Mg,Mn, Fe,Co, Ni) double perovskites

B-site rock salt-type ordered Sr₂MMoO₆ (M = Mg, Mn, Fe, Co, Ni) oxides have been systematically investigated in terms of their crystal structure, oxygen non-stoichiometry, transport properties, thermal expansion and chemical stability. Structural evolution on temperature of the studied materials was interpreted on a basis of octahedra rotation, with I4/m → Fm-3m phase transition. In the case of P2₁/n → I4/m transformation recorded for Sr₂MnMoO₆, a region of coexistence of two phases was observed. The Fe-containing compound was found to possess very high electrical conductivity, around 1000 S cm⁻¹ in 5 vol.% H₂ in Ar, and small negative Seebeck coefficient. Studies show that Mn- and Fe-containing compounds are stable only in reducing conditions, Co- and Ni-containing ones are stable only in oxidizing conditions, while Sr₂MgMoO₆ remains stable in a wide range of oxygen partial pressures. Recorded power density of a button-type SOFC with Sr₂FeMoO₆-based anode was 0.32 W cm⁻² at 900 °C.     

Cryogenic magnetic properties and magnetocaloric effects (MCE) in B-site disordered RE2CuMnO6 (RE = Gd,Dy, Ho and Er) double perovskites (DP) compounds

In this paper, a detailed investigation with respect to the structural, cryogenic magnetic properties and magnetocaloric performances of RE₂CuMnO₆ (RE = Gd, Dy, Ho and Er) double perovskite (DP) compounds has been performed. All the RE₂CuMnO₆ compounds are confirmed to B-site disordered and crystallized in the GdFeO₃-type structure (Pnma space group, N 62, oP20). The magnetic transition temperatures (T_M) are found to be ~7.5 K for Gd₂CuMnO₆, ~12.1 K for Dy₂CuMnO₆, ~12.2 K for Ho₂CuMnO₆, and ~3.6 K for Er₂CuMnO₆, respectively. Moreover, for checking the magnetocaloric performances several vital parameters including -ΔS_M^max (peak value of magnetic entropy change, -ΔS_M), TEC (3) (temperature averaged -ΔS_M) and RCP (relative cooling powers) are evaluated to be 7.84, 7.73 J/kgK and 151.1 J/kg for Gd₂CuMnO₆, 5.69, 5.59 J/kgK and 180.9 J/kg for Dy₂CuMnO₆, 7.12, 7.05 J/kgK and 192.4 J/kg for Ho₂CuMnO₆, as well as 9.92, 9.60 J/kgK and 195.9 J/kg for Er₂CuMnO₆ under the magnetic field change ΔH = 5 T, respectively.     

Thermal,optical, dielectric and electrical transport properties of nano-structured Se95-xIn5Prx (x = 2, 4, and 6) glassy alloys

In the present study, Se_95-xIn₅Pr_x (x = 2, 4, and 6) alloys were prepared using the melt quench technique. X-ray diffraction (XRD) and Raman spectroscopy reveal that the glassy matrix of each sample consists of crystalline entities identified as a mixed phase of indium selenide (HCP) and praseodymium selenide (FCC). TEM images show that the crystalline entities are nanorods stuck to nanoparticles. The thermal stability and optical band gap (direct) decrease (1.974 eV to 1.425 eV) with Pr content. The dielectric constant and loss are maximums for x = 4 at any frequency and temperature (30°C-60 °C). AC conductivity follows the correlated barrier hopping (CBH) model (frequency exponent $s<1\text{,}$ and decreases with temperature) with non-intimate valence alteration pairs (NVPA) for x = 2 and 6, and intimate valence alteration pairs (IVPA) for x = 4. AC activation energy decreases with Pr concentration at all frequencies in the study range.     

Aliphatic polycarbonate synthesis by copolymerization of carbon dioxide with epoxides over double metal cyanide catalysts prepared by using ZnX2 (X = F, Cl, Br, I)

As means of the chemical fixation of carbon dioxide and the synthesis polycarbonates, copolymerizations of carbon dioxide with various epoxides, such as cyclohexene oxide, cyclopentene oxide and propylene oxide were investigated in the presence of double metal cyanide (DMC) catalysts. The DMC catalysts were prepared by reacting K₃Co(CN)₆ with ZnX₂ (X = F, Cl, Br, I) together with tertiary butyl alcohol and poly(tetramethylene ether glycol) as complexing reagents and were characterized by various spectroscopic methods. The DMC catalysts showed high activity for epoxides and CO₂ copolymerization to yield aliphatic polycarbonates of narrow polydispersity and moderate molecular weight.