Tunnel-structured willemite Zn2SiO4: Electronic structure, elastic, and thermal properties

Abstract

Willemite Zn2SiO4 crystallizes in such a way that Zn and Si are tetrahedrally coordinated with O in an ionic-covalent manner to form ZnO4 and SiO4 tetrahedra as the building units. The tetrahedra are corner-sharing, of which one SiO4 tetrahedron connects eight ZnO4 tetrahedra, and one ZnO4 tetrahedron links four ZnO4 tetrahedra and four SiO4 tetrahedra. The unique crystallographic configuration gives rise to parallel tunnels with a diameter of 5.7 Å along the c-axis direction. The tunnel structure of Zn2SiO4 definitely correlates with its interesting elastic and thermal properties. On the one hand, the elastic modulus, coefficient of thermal expansion (CTE), and thermal conductivity are low. Zn2SiO4 has low Vickers hardness of 6.6 GPa at 10 N and low thermal conductivity of 2.34 W/(m·K) at 1073 K. On the other hand, the elastic modulus and CTE along the c-axis are significantly larger than those along the a- and b-axes, showing obvious elastic and thermal expansion anisotropy. Specifically, the Young’s modulus along the z direction (Ez = 179 GPa) is almost twice those in the x and y directions (Ex = Ey = 93 GPa). The high thermal expansion anisotropy is ascribed to the empty tunnels along the c-axis, which are capable of more accommodating the thermal expansion along the a- and b-axes. The striking properties of Zn2SiO4 in elastic modulus, hardness, CTE, and thermal conductivity make it much useful in various fields of ceramics, such as low thermal expansion, thermal insulation, and machining tools.

Enhancement of Thermoelectric Performance in Robust ZnO‐Based Composite Ceramics Driven by A Stepwise Optimization Strategy

“…[ 57,58 ] The much wider bandgap of Zn 2 SiO 4 than ZnO can act as the energy barrier to filter the low‐energy carriers, which will be discussed in detail later. Moreover, the unique tunnel structure of Zn 2 SiO 4 result in a low elastic modulus, which cause a low average sound velocity and a lower Debye temperature of 419 K. [ 59 ] Thus, the low average sound velocity predicts a low lattice thermal conductivity. Based on the Clarke model, the minimum thermal conductivity of Zn 2 SiO 4 is calculated to be only 1.04 W m −1 K −1 , [ 60 ] which contributes a lot to the ultralow κ l of 1.39 W m −1 K −1 in this work.…”

“…can benefit to enhance the mechanical performance of ZnO ceramic. [ 59 ] Hence, the Zn 2 SiO 4 plays an important role in enhancing TE and mechanical performance of ZnO ceramic simultaneously.…”

“…What's more, a higher Vickers hardness of 6.6 GPa at a load of 10 N of Zn 2 SiO 4 ceramic than ZnO ceramic reported by Dai et al can benefit to enhance the mechanical performance of ZnO ceramic. [59] Hence, the Zn 2 SiO 4 plays an important role in enhancing TE and mechanical performance of ZnO ceramic simultaneously. 3c, the grains are refined caused by the doping.…”

The phase structure, thermodynamic properties, and dissolution behavior of Ca5Mg4V6O24

“…A new garnet‐type phase of Ca 5 Mg 4 V 6 O 24 was found in the roasted sample during the composite roasting with CaO/MgO‐acid leaching process 10,11 . The crystal structure, phase transition, and thermodynamic properties of the garnet‐type Ca 5 Mg 4 V 6 O 24 are critical and indispensable to accurately establish the overall heat and mass balances, identifying the reaction mechanism, and generate the phase diagrams during the composite roasting with CaO/MgO 12–16 . However, no thermodynamic properties of the Ca 5 Mg 4 V 6 O 24 are available in the literature and thermodynamic databases, such as FactSage, 17–19 Thermo‐Calc, 20 HSC, 21 and MTData 22 .…”

“…10,11 The crystal structure, phase transition, and thermodynamic properties of the garnet-type Ca 5 Mg 4 V 6 O 24 are critical and indispensable to accurately establish the overall heat and mass balances, identifying the reaction mechanism, and generate the phase diagrams during the composite roasting with CaO/MgO. [12][13][14][15][16] However, no thermodynamic properties of the Ca 5 Mg 4 V 6 O 24 are available in the literature and thermodynamic databases, such as FactSage, [17][18][19] Thermo-Calc, 20 HSC, 21 and MTData. 22 In addition, the solubility of the Ca 5 Mg 4 V 6 O 24 in water as well as its dissolution behavior and kinetics in sulfuric acid, which is essential in acid leaching step, 23 is still lacking and incomplete.…”