CdXO3 (X = C, Si, Ge, Sn, Pb) electronic band structures

Abstract

a b s t r a c tElectronic properties for a set of CdXO 3 (X = C, Si, Ge, Sn, Pb) crystals were investigated using the density functional theory (DFT) formalism considering both the local density and generalized gradient approximations, LDA and GGA, respectively. Hexagonal CdCO 3 and triclinic CdSiO 3 have indirect main energy band gaps while orthorhombic CdGeO 3 and CdSnO 3 exhibit direct interband transitions. Orthorhombic CdPbO 3 has a very small indirect band gap. The Kohn-Sham minimum electronic band gap oscillates as a function of the X ns level, changing from 2.94 eV (hexagonal CdCO 3 ; LDAÞ to 0.012 eV (orthorhombic CdPbO 3 ; LDA).Ó 2009 Elsevier B.V. All rights reserved.CdXO 3 (X = C, Si, Ge, Sn, Pb) crystals exhibit several polymorphs and have a wide range of applications. Starting with CdCO 3 , nanoparticles were synthesized through the sonochemical method [1], and shape-controlled hydrothermal synthesis of single-crystalline hexagonal CdCO 3 nanowires, nanobelts, nanorolls, and other onedimensional nanostructures was achieved [2], with the possibility of transforming them into oriented nanoporous CdO. An aragonitetype phase was also found for CdCO 3 by Liu and Lin [3]. Cadmium silicate (CdSiO 3 ), on the other hand, is used as a host matrix for rare-earth doping, allowing for the production of multicolored long-lasting phosphorescence materials [4]. X-ray diffraction data for CdSiO 3 samples revealed a phase structure similar to that of pseudowollastonite CaSiO 3 (JCPDS 35-0810). A survey on the reported unit-cell parameters and space groups for pseudowollastonite CaSiO 3 published by Yang and Prewitt [5] mentions several works favoring either monoclinic or triclinic symmetries. Due to the resemblance between the pseudowollastonite CaSiO 3 and CdSiO 3 , Lei et al. [6] have argued that the crystal structure of the latter is expected to be an one-dimensional chain of edge-sharing SiO 4 tetrahedra.Cadmium germanate ðCdGeO 3 Þ at room temperature and atmospheric pressure has a complex structure resembling the pyroxenoids. Four CdGeO 3 polymorphs in the temperature range from 600°C to 1200°C and varying pressure up to 12 GPa were found by Susaki [7]. The pyroxenoid phase ðCdGeO 3 IÞ is transformed successively into garnet ðCdGeO 3 IIÞ, ilmenite (CdGeO 3 III, hexagonal) and perovskite (CdGeO 3 IV, orthorhombic with increasing pressure. The orthorhombic perovskite phase has Pbnm symmetry, with each germanium (coordination number IV) atom connected to six oxygen atoms, forming a tridimensional array of GeO 6 tilted octahedra with cadmium atoms inserted between them [8]. In order to understand the mechanisms behind the stabilization of the various perovskite crystals, CdGeO 3 , CaGeO 3 , CaSiO 3 , MgSiO 3 and other ABO 3 structures have been investigated [9]. Cadmium stannate ðCdSnO 3 Þ is a semiconducting oxide with gas-sensing properties [10][11][12], and experimental electronic energy band gap of 3.0 eV. Refinement of the CdSnO 3 structure confirms that it is a distorted orthorhombic perovskite, isostructura...

Structural, electronic and optical properties of ilmenite and perovskite CdSnO3from DFT calculations

“…For example, the ilmenite GGA-PBE band gap using ultrasoft pseudopotentials was 0.78 eV while the LDA band gap was 0.98 eV, while for perovskite we have found a GGA-PBE energy gap of only 0.42 eV and a LDA gap of 1.14 eV. These values were presented recently in a comparative study of CdXO 3 electronic band structures published by the authors [43].…”

Synergistic Effect on the Improved Electrochemical Performance in the Case of Fe1–xCdxCO3

“…Figure b displays the position of valence band maximum and conduction band minimum of FeCO 3 , Fe 5/6 Cd 1/6 CO 3 , and CdCO 3 . The band gaps of FeCO 3 and CdCO 3 are 3.448 and 5.749 eV, respectively, which are consistent with the previous reports. , While the band gap of Fe 5/6 Cd 1/6 CO 3 is 3.539 eV, suggesting that Fe 5/6 Cd 1/6 CO 3 possesses the similar band gap to FeCO 3 and maintains the electronic structure with good electric conductivity, as evidenced by the total and partial electronic densities of states in Figure c. This is also one reason for the improved electrochemical performance of Fe 0.8 Cd 0.2 CO 3 in Fe 1– x Cd x CO 3 composites.…”

Synthesis, Characterization, and Stability Studies of Ge-Based Perovskites of Controllable Mixed Cation Composition, Produced with an Ambient Surfactant-Free Approach

“…Indeed, with band gaps capable of being tailored to values lower than 2.0 eV, Ge-based perovskites have the potential to absorb light energy with wavelengths smaller than 610 nm (i.e., orange). As compared with Sn-based perovskites, theoretical calculations suggest that Ge-based perovskites are characterized by a more negative (i.e., more favorable) free energy of formation, thereby implying a greater stability of MAGeI 3 versus MASnI 3 , for instance Ge-based perovskites possess high ionic conductivity , and good electronic properties. , Ge is earth-abundant and evokes comparatively little toxicity or environmental concerns, thereby overcoming a major drawback of either Pb or Sn-based perovskites. Ge is much lighter than both Pb and Sn, a factor which should improve upon the power density of Ge-containing materials. Overall, Ge-based perovskites deserve further attention and effort. …”