Sn 5s Orbitals Research Articles

Structural, elastic, mechanical, and electronic properties of chalcogenide perovskite SnZrS3 under pressure

In this paper, we have presented the structural, elastic, mechanical, and electronic properties of the transition metal chalcogenide perovskite SnZrS3 under different pressures by using first-principles method. Our calculated lattice parameters at ambient pressure are in good agreement with the experimental and previous theoretical results. The elastic constants were evaluated numerically for orthorhombic SnZrS3 using the strain-stress approach. Orthorhombic SnZrS3 shows a strong anisotropic behavior of the elastic and structural properties. According to the calculations of the electronic properties, we find the states near the valence band top are derived from S 3p, Zr 4d, Sn 5p, and Sn 5s orbitals, and the lowest conduction band is composed of Zr 4d, S 3p, and Sn 5p orbitals. As the pressure increases, the conduction and valence band shift to lower and higher energies, respectively. These results indicated that lattice constants and band gap decrease with the increase of pressure.

First-principles study of halide double perovskite Cs2SnX6 (X=Cl, Br, I) for solar cell applications

In this work, we used different approximations, namely the GGA and LDA of the density functional theory framework, to investigate the properties of the double perovskite Cs2SnX6 ([Formula: see text], Br, I). We found that these materials are mechanically stable, and the calculated band gaps are 3.62[Formula: see text]eV for Cs2SnCl6, 2.33[Formula: see text]eV for Cs2SnBr6, and 1.00[Formula: see text]eV for Cs2SnI6, which agree well with the experimental results. The band structure reveals that the conduction band primarily arises from hybridization between the Sn-5s orbitals and the halogen p orbitals, while the valence band is predominantly composed of the halogen p orbitals. Additionally, we observed that all Cs2SnX6 compounds exhibit strong optical absorption in the ultraviolet region. Moreover, the absorption spectra edges shift toward the red from Cs2SnCl6 to Cs2SnI6. The thermoelectric properties have also been extensively characterized in this study. These favorable physical characteristics make Cs2SnX6 compounds attractive candidates for replacing expensive silicon cells in solar panels.

Structural Characteristics, Stability, and Electronic Properties of 001 Surface with Point Defects of Zinc Stannate: A First-Principle Study

This work presents first-principles calculations on the surface and defect impact upon zinc stannate (ZS) materials with perovskite bulk structures. The structure and electronic properties of both a perfect 001 surface and surfaces with a point defect of ZS were investigated by means of density functional theory calculations. The cohesive energies of a perfect 001 surface and those with O, Sn, or Zn defects were decreased compared with that of bulk ZS. Oxygen defects on the 001 surface of ZS formed more easily than others based on the obtained cohesive energy and defect formation energy. The electronic properties close to the Fermi levels of bulk ZS materials were mainly controlled by the O 2p and Sn 5s orbitals. The formation of vacancy on the 001 surface of ZS changed the band structure and band gap compared with that of the bulk. The modulation mechanism was explored by means of structure transformation, band structure, and density of states analysis.

Simultaneous enhancement in electrical conductivity and Seebeck coefficient by single- to double-valley transition in a Dirac-like band

SnTe possesses a single- to double-valley transition in the conduction band minimum when a compressive strain is applied. Through a tight-binding analysis, it is shown that the variation of the band structure is attributed to the strain-induced delocalization of both the Sn-5s orbitals and Te-5p orbitals with different angular momenta. This effect can largely increase the electron density of states near the band edge and thus keep the Fermi level of the compressed SnTe closer to it, where the electrons have lower scattering rates. The strain-induced double valleys lead to simultaneous increases in the electrical conductivity and the Seebeck coefficient and thereby nearly four times the enhancement of the power factor at the doping concentration of 5×1019 cm–3. This work suggests a feasible concept that can be employed to promote the power factor of a Dirac semiconductor via manipulating the valley degeneracy in the conduction band minimum.

Effect of Sb substitution on structural, morphological and electrical properties of BaSnO3 for thermoelectric application

Sb-substituted BaSnO3 (BSO) perovskite microstructures were synthesized by a polymerization complex method with Sb concentrations of 0, 1, 5, and 10 mM. The electronic band structures of pure BSO and Sb-substituted BSO were theoretically verified by density functional theory. The findings indicated that the conduction band property was primarily attributed to the Sb-5s and Sn-5s orbitals. The Sb5+ donor and the subsequent oxygen vacancy enhanced electronic conduction. A high Seebeck coefficient of 58.9 μV/K and power factor of 2.1 μWm−1K−2 were achieved for the 10 mM Sb-substituted BSO at 820 K. The semiconductor to metallic transition was observed at 700 K owing to the charge compensation between Sb5+ and Sn4+ ions. The structural defects and grain boundaries contributed to a low thermal conductivity in the samples. The 10 mM Sb-substituted BSO sample exhibit the dimensionless figure of merit of 0.28 × 10−2 at 820 K.

Material Design of New p-Type Tin Oxyselenide Semiconductor through Valence Band Engineering and Its Device Application.

This paper reports a new p-type tin oxyselenide (SnSeO), which was designed with the concept that the valence band edge from O 2p orbitals in the majority of metal oxides becomes delocalized by hybridizing Se 4p and Sn 5s orbitals. As the Se loading increased, the SnSeO film structures were transformed from tetragonal SnO to orthorhombic SnSe, which was accompanied by an increase in the amorphous phase portion and smooth morphologies. The SnSe0.56O0.44 film annealed at 300 °C exhibited the highest Hall mobility (μHall), 15.0 cm2 (V s)-1, and hole carrier density (nh), 1.2 × 1017 cm-3. The remarkable electrical performance was explained by the low hole effective mass, which was calculated by a first principle calculation. Indeed, the fabricated field-effect transistor (FET) with a p-channel SnSe0.56O0.44 film showed the high field-effect mobility of 5.9 cm2 (V s)-1 and an ION/OFF ratio of 3 × 102. This work demonstrates that anion alloy-based hybridization provides a facile route to the realization of a high-performance p-channel FET and complementary devices.

Detection of intra-band gap defects states in spin-coated sol-gel SnOx nanolayers by photoelectron spectroscopies

The presence of occupied intra-band gap states in oxygen-deficient tin dioxide (SnOx; 1 < x < 2) is crucial for efficient manufacturing of multipurpose electronic devices based on transparent conducting oxides. Former experimental determination of these states was conducted for well-defined, usually thick tin oxides obtained under highly controlled vacuum conditions. In this work, we present precise specification of gap defects states for ultra-thin SnOx layers prepared by sol-gel synthesis followed with spin-coat deposition. Post-deposition drying and annealing processing changed layers’ surface morphology and bulk crystalline structure as monitored by scanning electron microscopy, atomic force microscopy and x-ray diffraction. An x-ray photoemission spectroscopy (XPS) analysis of chemical composition revealed the presence of both Sn2+ and Sn4+ species in layers with and without post-drying annealing step. A stronger contribution of SnO was found for dried SnOx. In the valence band region, XPS studies revealed pronounced O 2p and hybridised Sn 5p/5s–O 2p states as well as deep, overlapping with the O 2p, band gap states resulting from Sn 5s orbitals. These states—attributed to defect states—indicated enhanced presence of Sn2+ cations, and were assigned to ‘bridging’ oxygen vacancies. Complementary photoemission yield spectroscopy (PYS) studies of the SnOx band gap region revealed an increased effective density of occupied electronic states below the Fermi level EF for annealed layers. The consequence was a work function reduction by 0.15 eV after the annealing process. PYS results allowed a precise detection of SnOx shallow band gap states close to EF. These states were attributed to surface oxygen vacancies, which was confirmed by computer modelling. Finally, the annealed layers exhibited higher calculated charge carrier concentration, hence the increased n-type character.

First-principles investigations on the mechanical, thermal, electronic, and optical properties of the defect perovskites Cs2SnX6 (X = Cl, Br, I)**Project supported by the National Natural Science Foundation of China (Grant Nos. 51572219 and 11447030), the Natural Science Foundation of Shaanxi Province of China (Grant No. 2015JM1018), and Graduate’s Innovation Fund of Northwest University of China (Grant No. YJG15007).

The mechanical properties, thermal properties, electronic structures, and optical properties of the defect perovskites Cs2SnX6 (X = Cl, Br, I) were investigated by first-principles calculation using PBE and HSE06 hybrid functional. The optic band gaps based on HSE06 are 3.83 eV for Cs2SnCl6, 2.36 eV for Cs2SnBr6, and 0.92 eV for Cs2SnI6, which agree with the experimental results. The Cs2SnCl6, Cs2SnBr6, and Cs2SnI6 are mechanically stable and they are all anisotropic and ductile in nature. Electronic structures calculations show that the conduction band consists mainly of hybridization between the halogen p orbitals and Sn 5s orbitals, whereas the valence band is composed of the halogen p orbitals. Optic properties indicate that these three compounds exhibit good optical absorption in the ultraviolet region, and the absorption spectra red shift with the increase in the number of halogen atoms. The defect perovskites are good candidates for probing the lead-free and high power conversion efficiency of solar cells.

Sn(II)-Containing Phosphates as Optoelectronic Materials

We theoretically investigate Sn(II) phosphates as optoelectronic materials using first principles calculations. We focus on known prototype materials Sn$_n$P$_2$O$_{5+n}$ (n=2, 3, 4, 5) and a previously unreported compound, SnP$_2$O$_6$ (n=1), which we find using global optimization structure prediction. The electronic structure calculations indicate that these compounds all have large band gaps above 3.2 eV, meaning their transparency to visible light. Several of these compounds show relatively low hole effective masses ($\sim$2-3 m$_0$), comparable the electron masses. This suggests potential bipolar conductivity depending on doping. The dispersive valence band-edges underlying the low hole masses, originate from the anti-bonding hybridization between the Sn 5s orbitals and the phosphate groups. Analysis of structure-property relationships for the metastable structures generated during structure search shows considerable variation in combinations of band gap and carrier effective masses, implying chemical tunability of these properties. The unusual combinations of relatively high band gap, low carrier masses and high chemical stability suggests possible optoelectronic applications of these Sn(II) phosphates, including p-type transparent conductors. Related to this, calculations for doped material indicate low visible light absorption, combined with high plasma frequencies.

Role of Sn2+ in the Band Structure of SnM2O6 and Sn2M2O7(M = Nb and Ta) and Their Photocatalytic Properties

The photocatalytic properties of metal oxides consisting of Sn2+ with a 5s2 configuration were studied to find new visible light responsive photocatalysts. The band gaps of Ca2Ta2O7, Sn2Ta2O7, and Sn2Nb2O7 were found to be 4.8, 3.0, and 2.3 eV, respectively. Density functional calculations revealed that the valence band levels formed with Sn 5s orbitals were more negative than those with O 2p orbitals. The result is that niobates and tantalates containing Sn2+ have narrow band gaps compared with typical niobates and tantalates. SnNb2O6 showed photocatalytic activity for H2 and O2 evolution from aqueous solutions containing sacrificial reagents (methanol and Ag+) under visible light irradiation (λ > 420 nm). Moreover, the photocatalytic activity of SnNb2O6 depended on the material used as the Sn source. SnNb2O6 synthesized from Sn3O2(OH)2 showed higher activity for H2 and O2 evolution than that synthesized from commercial SnO, which included a small amount of SnO2. SnNb2O6 synthesized from Sn3O2(OH)2 showe...

Energy Structure and Photocatalytic Activity of Niobates and Tantalates Containing Sn(II) with a 5s2 Electron Configuration

Abstract SnNb2O6 (BG = 2.3 eV) containing Sn2+ with a 5s2 electron configuration showed the photocatalytic activity for H2 evolution from an aqueous methanol solution under visible light irradiation (λ &amp;gt; 420 nm) in the presence of a Pt cocatalyst. The energy structure calculation by the plane wave based density functional method revealed that the conduction and valence bands consisted of Nb4d and Sn5s orbitals, respectively. The valence band level consisting of the Sn5s orbitals was more negative than that consisting of O2p orbitals resulting in SnNb2O6 being responsive to visible light.

A cluster approach for the SnO 2 (110) face

Some results are given from a cluster approach for the electronic structure of the SnO 2 (110) face together with some oxygen vacancies and ‘adsorbates’. Computations are based on ab initio methods, the local-density approximation and atomic orbitals as a basis set. Solutions were calculated self-consistently, but also using a composition of atomic potentials (for some smaller clusters). The atomic-orbital nature (origin) of the cluster levels was traced by projection onto the atomic bases set. The results here refer to a basic cluster [SnO 2 13 with 17 surface atoms moedelling the SnO 2 (110) face and the other 22 atoms in the next five suface layers. The effect of oxyggen ’adsrobates‘ and oxygen vacancies in the few uppermost subsurface layers on the electronic structure was considered. In particular, the focus was on the levels related to oxygen vacancies and originating from Sn 5s orbitals, which are well-known donor levels in the deep bulk, making SnO 2 an n-type semiconductor. The results support some other theoretical and experimental predictions that oxygen vacancies behave as neutral defects at or near SnO 2 surfaces.