Search

The thermal transport properties of minerals at high temperature and high pressure are important for understanding the internal evolution and dynamic processes of the Earth. Here, we carry out a detailed study on the lattice thermal conductivities ( κ latt ) of Mg 2 SiO 4 under upper mantle and transition zone conditions by anharmonic lattice dynamics method. The calculations show that the κ latt of Mg 2 SiO 4 increase with the phase transitions, which agree with the previous measurements and are attributed to the increase of lifetime and group velocity under extreme conditions. The κ latt of Mg 2 SiO 4 along the geotherm shows a 64 % jump at 410 km and 71 % jump at 520 km . The anisotropy in the κ latt of olivine and wadsleyite decreases with increasing pressure. The present findings offer a fundamental knowledge of the κ latt of Mg 2 SiO 4 under extreme conditions, which are crucially important for understanding the thermal transport processes in the Earth. [ABSTRACT FROM AUTHOR]

We present a stoichiometry-dependent structural phase transition in SrRuO3 film on SrTiO3 substrate. The oxygen stoichiometry in the films was varied by changing the oxygen partial pressure P(O2) during the deposition process. For SrRuO3 films with P(O2) ≥ 60 mTorr, they exhibited a pseudo-orthorhombic structure with in-plane uniaxial magnetic anisotropy. On the other hand for films with P(O2) ≤ 45 mTorr, the tetragonal SrRuO3 phase with a perpendicular uniaxial magnetic anisotropy was stabilized at room temperature. The big difference in the magnetic anisotropy of these two SrRuO3 phases was shown to be closely linked to their respective RuO6 octahedral rotation patterns: the RuO6 octahedra rotate differently along the two orthogonal in-plane directions in the pseudo-orthorhombic phase, whereas in the tetragonal phase only octahedral rotations around z-axis are present and the octahedral tilts along the in-plane axes are diminished. First-principles calculations show that such a suppression of the RuO6 octahedra tilting in the tetragonal phase arises from the oxygen vacancies at the octahedral apex (along z-axis). This work demonstrates that the stoichiometry plays an important role in determining the octahedral rotations and tilts in the perovskite materials, which may induce new phases with distinctively different structural symmetry and physical property. [ABSTRACT FROM AUTHOR]

Transition metal (TM) modification is a common strategy for converting an earth-abundant mineral into a cost-effective catalyst for industrial applications. Among a variety of minerals, Al2SiO5, which has three phases, andalusite, sillimanite and kyanite, is emerging as a promising candidate for new catalyst development. In this paper, we use Mn to demonstrate the rationale of 3d TM doping at the Al sites in each of these three phases through first-principles calculations and the cluster expansion method. The results of cluster expansion show that Mn has a strong site preference for the six-coordinated Al octahedral chains in the andalusite and sillimanite phases, while distributing randomly in the kyanite phase. Moreover, Mn can only replace Al in sillimanite and kyanite in low concentrations; however, higher concentrations of Mn can replace Al in andalusite. We found that the concentration sensitivity is due to the Jahn–Teller distortion and 3d orbital splitting. This finding can also explain the low doping concentrations of other 3d TMs (Fe, Cr and V) in Al2SiO5 compounds. Based on the calculated Helmholtz free energy, we constructed a (MnxAl1−x)AlSiO5 temperature-composite phase diagram, which explains the physical mechanisms behind the results for 3d transition metal doping and phase transitions in Al2SiO5. This work could shed light on the related physics, chemistry, and geoscience of (MnxAl1−x)AlSiO5, and more importantly, a design rationale for the engineering of cheap catalysts. [ABSTRACT FROM AUTHOR]

We used the CASTEP program with a GGA+ U method to study the effects of Cu doping on the formation energy, electronic and optical properties of V-doped ZnO. The calculated enthalpies show that Cu inclines stay near V. The formation energy shows Cu and V codoping is easy to form in an oxygen atmosphere. Vanadium introduces an impurity band level and Cu widen the level. The relation between the band and density of states (DOS) has been discussed. The calculated absorption coefficient ( α( ω)) shifts to lower energy (red shift). The absorption coefficient also has a broad increased peak in the green energy region (around 530 nm). We also calculated the other optical constants of Cu and V codoped ZnO. The relation between the optical properties and DOS has been discussed. Our calculations not only can explain the experiment and but also clarify the mechanism and role of Cu on the optical properties of V-doped ZnO. Our study provides a reference and method for improving codoping content and absorption in the visible region of V-doped ZnO. We also provide a reference in designing optical devices base on V-doped ZnO. [ABSTRACT FROM AUTHOR]

In this study, density-functional theory plane-wave pseudopotential method was employed to investigate several oxygen vacancies on TiO2 anatase (101) surface. At first, a suitable defect-free slab model has been established by analyzing the surface energies and the atomic relaxations influenced by different technical parameters. The formation energies of different kinds of oxygen vacancies in the outermost layer have also been compared as well as the atomic displacement of the defective surfaces. It was found that the presence of bridging oxygen vacancy is more energetically favored and causes larger atomic displacement than other types of surface oxygen vacancies. The reactivity of oxygen vacancies has also been tested by both molecular and dissociated oxygen adsorption. Furthermore, we discussed the configurations and the electronic properties of O2-adsorbed surface, and found that the appearance of oxygen adsorbate-induced states in the band gap can make the surface sensitive to visible light. [ABSTRACT FROM AUTHOR]

The effect of the Zn/Sn ratio in the solution on the properties of Cu 2 ZnSnS 4 films prepared by sol-gel method has been investigated. As the Zn/Sn ratio in the solution increases to a certain value, a pure single phase kesterite CZTS is obtained and confirmed by XRD, XPS and Raman. Through controlling the Zn/Sn ratio in the solution, secondary phases such as SnO 2 can be avoided and an optimal condition for single phase kesterite CZTS can be achieved. Surface SEM images of the CZTS films are investigated and the optical band gap of the optimized CZTS film is found to be 1.23 eV. [ABSTRACT FROM AUTHOR]

The thermal transport properties of mantle minerals are of paramount importance to understand the thermal evolution processes of the Earth. Here, we perform extensively structural searches of two-dimensional MgSiO 3 monolayer by CALYPSO method and first-principles calculations. A stable MgSiO 3 monolayer with Pmm 2 symmetry is uncovered, which possesses a wide indirect band gap of 4.39 eV. The calculations indicate the lattice thermal conductivities of MgSiO 3 monolayer are 49.86 W (mK) -1 and 9.09 W (mK) -1 in x and y directions at room temperature. Our findings suggest that MgSiO 3 monolayer is an excellent low-dimensional thermoelectric material with high ZT value of 4.58 from n-type doping in the y direction at 2000 K. The unexpected anisotropic thermal transport of MgSiO 3 monolayer is due to the puckered crystal structure and the asymmetric phonon dispersion as well as the distinct electron states around the Fermi level. These results offer a detailed description of structural and thermal transport properties of MgSiO 3 monolayer at extreme conditions., (© 2024 IOP Publishing Ltd.)