SnO2: A comprehensive review on structures and gas sensors

Abstract In situ x-ray data on molar volumes of periclase and tungsten have been collected over the temperature range from 300 K to melting. We determine the temperature by combining the technique of spectroradiometry and electrical resistance wire heating. The thermal expansion (α) of periclase between 300 and 3100 K is given by α=2.6025 10−5+1.3535 10−8 T+6.5687 10−3 T−1−1.8281 T−2.For tungsten, we have (300 to 3600 K) α=7.862 10−6+6.392 10−9 T.The data at 298 K for periclase is: molar volume 11.246 (0.031) cm3, α=3.15 (0.07) 10−5 K−1, and for tungsten: molar volume 9.55 cm3, α=9.77 (10.08) 10−6 K−1.

Thermal expansion of periclase (MgO) and tungsten (W) to melting temperatures Sample: T = 298 K

An economic and environmentally friendly catalyst derived from waste freshwater mussel shell (FMS) was prepared by a calcination-impregnation-activation method, and it was applied in transesterification of Chinese tallow oil. The as-prepared catalyst exhibits a “honeycomb” -like structure with a specific surface area of 23.2 m2 g−1. The newly formed CaO crystals are major active phase of the catalyst. The optimal calcination and activity temperature are 900 °C and 600 °C, respectively. When the reaction is carried out at 70 °C with a methanol/oil molar ratio of 12:1, a catalyst concentration of 5% and a reaction time of 1.5 h, the FMS-catalyst is active for 7 reaction cycles, with the biodiesel yield above 90%. The experimental results indicate that the FMS can be used as an economic catalyst for the biodiesel production.

Utilization of waste freshwater mussel shell as an economic catalyst for biodiesel production

Laves phases with their comparably simple crystal structure are very common intermetallic phases and can be formed from element combinations all over the periodic table resulting in a huge number of known examples. Even though this type of phases is known for almost 100 years, and although a lot of information on stability, structure, and properties has accumulated especially during the last about 20 years, systematic evaluation and rationalization of this information in particular as a function of the involved elements is often lacking. It is one of the two main goals of this review to summarize the knowledge for some selected respective topics with a certain focus on non-stoichiometric, i.e., non-ideal Laves phases. The second, central goal of the review is to give a systematic overview about the role of Laves phases in all kinds of materials for functional and structural applications. There is a surprisingly broad range of successful utilization of Laves phases in functional applications comprising Laves phases as hydrogen storage material (Hydraloy), as magneto-mechanical sensors and actuators (Terfenol), or for wear- and corrosion-resistant coatings in corrosive atmospheres and at high temperatures (Tribaloy), to name but a few. Regarding structural applications, there is a renewed interest in using Laves phases for creep-strengthening of high-temperature steels and new respective alloy design concepts were developed and successfully tested. Apart from steels, Laves phases also occur in various other kinds of structural materials sometimes effectively improving properties, but often also acting in a detrimental way.

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Laves phases: a review of their functional and structural applications and an improved fundamental understanding of stability and properties

The ground- and metastable-state properties of II-VI oxides in wurtzite (h-MgO), zincblende and rocksalt structures are systematically investigated using first-principles. We study the phase stability of these three structures energetically, and find that CaO, SrO and BaO prefer h-MgO instead of wurtzite. This is consistent with the fact that ionic compounds prefer a high coordination. We also examine the influence of the crystallographic structure and cations on elastic constants, bulk moduli, spontaneous polarisation, piezoelectricity, band structures and optical properties. The band offsets for the common semiconductors (BeO, MgO, ZnO and CdO) in the zincblende structure are calculated. Our calculated results are in good agreement with other theoretical and experimental data.

First-principles study of ground- and metastable-state properties of XO (X = Be, Mg, Ca, Sr, Ba, Zn and Cd)

In this paper, the thermoelectric (TE) properties of Janus MXY monolayers (M = Pd, Pt; X, Y = S, Se, Te) are systematically studied using first principles and the Boltzmann transport theory. The thermal conductivity (k), Seebeck coefficient (S), power factor (PF), and TE figure of merit (ZT) are calculated accurately for various carrier concentrations. The lattice thermal conductivities of these six materials sequentially decrease in the order PtSSe, PtSTe, PtSeTe, PdSSe, PdSTe, and PdSeTe. PdSeTe and PtSeTe monolayers have a high ZT close to one at 300 K. In addition, we predicted the TE properties at high temperatures and found that the maximum ZT (2.54) is achieved for a monolayer of PtSeTe at 900 K. The structural and electronic properties of these six Janus transition-metal dichalcogenide (TMD) monolayers were systematically studied from first principles. Our results show that all six materials are semiconductors with bandgaps between 0.77 eV and 2.26 eV at the Heyd-Scuseria-Ernzerhof (HSE06) level. The present work indicates that the Janus MXY TMD monolayers (M = Pd, Pt; X, Y = S, Se, Te) are potentially TE materials.

Thermoelectric properties of Janus MXY (M = Pd, Pt; X, Y = S, Se, Te) transition-metal dichalcogenide monolayers from first principles

The equations of state (EOS) and other thermodynamic properties of the rocksalt (RS) structure MgO are investigated by ab initio plane-wave pseudopotential density functional theory method. The obtained results are consistent with the experimental data and those calculated by others. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of relative volume V/V-0 on pressure P, cell volume V on temperature T, and Debye temperature Theta and specific heat C-V on pressure P are successfully obtained. The variation of the thermal expansion alpha with temperature and pressure is investigated, which shows the temperature has hardly any effect on the thermal expansion alpha at higher pressure. (c) 2005 Elsevier B.V. All rights reserved.

Thermodynamic properties of MgO under high pressure from first-principles calculations

The phase transition of SiC from the zinc blende (ZB) structure to the rocksalt (RS) structure under pressure is investigated by the first principles plane-wave pseudopotential density functional theory method. The results obtained are in good agreement with the experimentally measured data and other theoretically calculated results. It is found that the pressures of transition of SiC from the ZB structure to the RS structure are 74.6 GPa from total energy–volume data and 75.4 GPa from the enthalpy calculations. Moreover, through the quasi-harmonic Debye model, in which the phononic effects are considered, the dependences of relative volume V/V0 on pressure P at T=0, 1400 K are successfully obtained. The calculated volume reduction at the transition is 18%. In particular, from the high-pressure elastic constants obtained, the ZB structure SiC is found unstable when the applied pressure is larger than 126.6 GPa. This value is in excellent agreement with the experimental data and the molecular dynamics (MD) simulation results.

First-principles study of pressure-induced phase transition in silicon carbide

The structural B1-B2 phase transition of CaO and the elastic properties of the B1 phase of CaO are investigated by ab initio plane-wave pseudopotential density functional theory method. The dependences of the elastic constants c(ij), the aggregate elastic modulus B-s and G, the elastic anisotropic parameter A, and the Debye temperature Theta(D) on pressure are successfully discussed. From the usual condition of equal enthalpies, we find that the structural B1-B2 phase transition of CaO occurs at 62.8GPa, consistent with the experimental value 61 GPa. From our elastic constants of CaO under pressure, we find that the B1-B2 structural transformation occurs at about 178 GPa by the elastic instability, which is far higher than the transition pressure 62.8 GPa. (c) 2006 Elsevier B.V. All rights reserved.

Phase transition and elastic constants of CaO from first-principle calculations

We investigate the structural, phase transition and elastic properties of SnO(2) in the rutile-type, pyrite-type, ZrO(2)-type and cotunnite-type phases by the plane-wave pseudopotential density functional theory method. The lattice constants, bulk modulus and its pressure derivative are well consistent with the available experimental and other theoretical data. Also, we find that the rutile -> pyrite, pyrite -> ZrO(2) and ZrO(2)-> cotunnite phase transition occur at 12.9, 59.1 and 111.1 GPa, which are in better agreement with the experimental results than those of Gracia et al. (2007). Moreover, we obtain the pressure dependences of elastic constants for the four structures. (C) 2011 Elsevier B. V. All rights reserved.

Jun Zhu

Papers

Thermoelectric properties of Janus MXY (M = Pd, Pt; X, Y = S, Se, Te) transition-metal dichalcogenide monolayers from first principles

Thermodynamic properties of MgO under high pressure from first-principles calculations

First-principles study of pressure-induced phase transition in silicon carbide

Phase transition and elastic constants of CaO from first-principle calculations

Structures, phase transition, elastic properties of SnO 2 from first-principles analysis