Theoretical study of electronic properties and chemical stability of cubic phase zirconia nanowires

Zirconia bulk is one of the most studied materials around the world due to different properties such as a high melting temperature, biocompatibility, and high thermal expansion, among many others. However, there is little experimental research about Zirconia nanowires and until now there are few theoretical papers on the subject. In this work, DFT calculations on bare ZrO2 nanowires with diameter variation were performed. In order to get the more accurate parameters for calculation on nanowires, we employed the Murnaghan equation of state in a cubic phase of ZrO2 and we compared the results obtained with some experimental data as well as the lattice parameter and the bulk modulus. The nanowires were grown along with the [1 1 1] direction with five different diameters. All calculations were carried out by Density Functional Theory (DFT) implemented in SIESTA code. According to our results, GGA-PBE is the more accurate functional for describing the Exc on ZrO2. The calculation of formation and surface energies shows that these nanowires are highly stable chemically. Furthermore, nanowires larger than 8.78 ˚A present a direct bandgap. These results indicate the possibility of applying ZrO2 nanowires in the optoelectronic field.

New triple molybdate and tungstate Na5Rb7Sc2(XO4)9 (X = Mo, W)

New compounds of the composition Na5Rb7Sc2(XO4)9 (X = Mo, W) were obtained via the ceramic technology. The sequences of chemical transformations occurring during the formation of these compounds were established, and their primary characterization was performed. Both Na5Rb7Sc2(XO4)9 (X = Mo, W) were found to melt incongruently at 857 K (X = Mo) and 889 K (X = W). They are isostructural to Ag5Rb7Sc2(XO4)9 (X = Mo, W), Na5Cs7Ln2(MoO4)9 (Ln = Tm, Yb, Lu) and crystallize in the trigonal crystal system (sp. gr. R32). The crystal structures were refined with the Rietveld method using the powder X-ray diffraction data. The thermal expansion of Na5Rb7Sc2(WO4)9 was studied by high-temperature powder X-ray diffraction; it was shown that this triple tungstate belongs to high thermal expansion materials.

Structures, and Thermophysical Properties Characterizations of (La1-xHox)3NbO7 Solid Solutions as Thermal Barrier Coatings

A sequence of (La1-xHox)3NbO7 solid solutions were fabricated in this work, which were studied as candidate for thermal insulation materials. The lattices were identified via XRD, when SEM and EDS were used to characterize the microstructures and element distributions. The results showed that the highest modulus, hardness, and toughness of (La1-xHox)3NbO7 were 196 GPa, 9.2 GPa, and 1.6 MPa m1/2, respectively, and they accorded with the mechanical property requirements. Also, a low thermal conductivity (1.06 W m−1 K−1) and high thermal expansion coefficients (TECs: 11.3 × 10−6 K−1) were simultaneously realized in (La3/6Ho3/6)3NbO7, at high temperatures. No phase transition was detected up to 1,200°C, which proved their good high-temperature lattice stability. The intense anharmonic lattice vibrations might contribute to the outstanding thermal properties of (La1-xHox)3NbO7 ceramics. The suitable modulus, high hardness, low thermal conductivity, and high TECs of (La1-xHox)3NbO7 solid solutions proclaimed that they were exceptional thermal insulation ceramics.

(ECS Meeting PRiME 2020) High TEC copper to connect copper bond pads for low temperature wafer bonding

Copper to copper wafer hybrid bonding is the most promising technology for three-dimensional (3D) integration. In the hybrid bonding process, two silicon wafers are aligned and contacted. At room temperature, these aligned copper pads contain radial-shaped nanometer-sized hollows due to the dishing effect induced by chemical-mechanical polishing (CMP). These wafers are annealed for copper to expand and connect upper and lower pads. This copper expansion is key to eliminate the radial-shaped hollows and make copper pads contacted. Therefore, in this research, we investigated the new high thermal expansion coefficient (TEC) electrodeposited copper to eliminate dishing hollows at lower temperature than that with conventional copper using the combination of new additive A and three other additives. The TEC of new electrodeposited copper is 25.2 x 10-6 oC-1, 46% higher than conventional copper and the calculated contact area of copper surface at 250oC with 5 nm dishing depth is 100%.

Low-Temperature Crystal Chemistry of Hingganite-(Y), from the Wanni Glacier, Switzerland

Hingganite from the Wanni glacier (Switzerland) was studied by means of energy dispersive and wavelength-dispersive spectroscopy, Raman spectroscopy, and low-temperature single-crystal X-ray diffraction. According to its chemical composition, the investigated mineral should be considered as hingganite-(Y). It showed a relatively high content of Gd, Dy, and Er and had limited content of lighter rare-earth element (REE), which is typical for Alpine gadolinite group minerals. The most intense Raman bands were 116, 186, 268, 328, 423, 541, 584, 725, 923, 983, 3383, and 3541 cm−1. Based on data of low-temperature [(−173)–(+7) °C] in situ single-crystal X-ray diffraction, it was shown that the hingganite-(Y) crystal structure was stable in the studied temperature range and no phase transitions occurred. Hingganite-(Y) demonstrated low volumetric thermal expansion (αV = 9(2) × 10−6 °C−1) and had a high thermal expansion anisotropy up to compression along one of the directions in the layer plane. Such behavior is caused by the shear deformations of its monoclinic unit cell.

Conductive vitrimer nanocomposites enable advanced and recyclable thermo-sensitive materials

Vitrimers with high thermal expansion rate were innovatively explored to produce advanced and recyclable thermo-sensitive conductive nanocomposites and sensors.

Intermetallic M Pt3 (M = Ti, Zr, Hf): Elastic, electronic, optical and thermal properties

In this study, the structural and unexplored elastic, electronic, optical and thermal properties of Pt-based alloys MPt3 (M = Ti, Hf) and only optical and thermal properties of ZrPt3 are subjected to investigation using the method of the first principles. The results of pressure dependence of mechanical and thermal properties are discussed. The electronic band structures and density of state data show metallic conductivity for all the compounds. The main contribution at Fermi level comes from Ti 3d and Zr 4d (for TiPt3 and ZrPt[Formula: see text] and Pt 5d (for HfPt[Formula: see text] orbitals. The materials’ optical reflectivity values, relatively high in the IR-visible-UV regions, range from [Formula: see text]62% to 72% in the visible region which show better performance values in comparison to those of some representative materials PtAl2, AuAl2 and GdX3 (X = In, Sn, Tl, Pb). The unexplored thermal behaviors are also investigated via quasi-harmonic Debye model at T = 0 and P = 0 as well as at elevated temperatures and pressures. In addition, when used as bonding materials, studied intermetallics with moderately high thermal expansion coefficients can match other substrates. This coupled with the estimated thermal conductivities (k[Formula: see text]) compared to several other species indicate that the intermetallics can be used in applications, such as thermal barrier coatings (TBC). This study has thus indicated possible alternative candidates for high-temperature applications which would initiate further research and development on the intermetallics under study.

Influence of Sm2O3 Additive on BaO-Al2O3-B2O3-SiO2 Glass-Ceramics for CBGA Package

Sm2O3 additive significantly influenced the microstructure, mechanical, and electrical properties of BaO-Al2O3-B2O3-SiO2 glass-ceramics. The calculation by the whole pattern fitting method based on XRD patterns revealed that Sm2O3 additive improved the crystallization process of this tetra-system and promoted the formation of major phase quartz. The sintering kinetics showed that Sm2O3 addition markedly reduced the sintering activation energy from 406.86 kJ/mol to 391.38 kJ/mol, which benefited the sintering densification and the grain growth, and thus enhanced mechanical properties. Doping 2% Sm2O3 reinforced the flexure strength from 136.3 to 171.6 MPa and the Young’s modulus from 49.4 to 79.7 GPa. It also exhibited low dielectric constant of 5.31, low dielectric loss of 5.30 × 10-4, and high thermal expansion coefficient of 11.76 × 10-6/°C.