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Ta–Si-C films were deposited by DC magnetron co-sputtering using TaC and Si targets in an Ar-discharge atmosphere. Increasing the current of Si target from 0.0 to 0.5 A led to a continuous increase of Si content from 0.0 to 30.8 at%. The effects of Si content on microstructure were systematically investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). At low Si content (≤ 5.6 at%), Si occupied C vacancies to form a solid solution Ta(C, Si). Further increasing the Si content, some Si atoms bonded with C atoms resulting in the formation of amorphous phase (a-C:Si), and the films presented a nanocomposite structure consisting of solid solution Ta(C, Si) surrounded by a-C:Si matrix. At the highest Si content (30.8 at%), the film exhibited finally X-ray amorphous structures. The hardness ( H ) and fracture toughness ( K f ) were observed to initially increase and then decrease as the Si content was increased. At 5.6 at% Si, the film exhibited a maximum in H (44.9 ± 2.7 GPa) and K f (3.61 ± 0.16 MPa m 1/2 ), which can be ascribed to the formation of a solid solution. On further increasing the Si content, an amorphous phase gradually appeared, leading to a decrease in H and K f . [ABSTRACT FROM AUTHOR]

Nd-doped BaTiO 3 ceramics with Ti vacancy compensation were prepared by a solid-state reaction method, and the lattice structures were identified by XRD and Raman spectra. Samples with light doping possess a tetragonal structure at room temperature, while the cubic phase appeared as the doping content increased. Dielectric properties at low temperature (−100–0 °C) were characterized by the dielectric constant, complex impedance and electric modulus. Colossal dielectric constant and dielectric relaxation processes appeared in all samples. Three electrical responses were observed in the low doping content ceramics, while four appeared in the high doping content ceramics by a combined plot of Z″ and M″. These responses were attributed to the microstructure inhomogeneity, which in turn can be ascribed to charge segregation when the doping content is high. Localization of charge carriers was also observed in all of the ceramics, and the confined carriers preferred to exist in the grain when the doping content was low, while localization would be more significant in grain boundaries with increased dopant. The localization could be ascribed to the formation of defect complexes, which on one hand maintained a high resistivity to the ceramics, and on the other hand, resulted in polarization of the dipoles. Both Maxwell-Wagner polarization and dipole polarization were found to exist in the Nd-doped BaTiO 3 ceramics and were responsible for the colossal dielectric constant and relaxations. The space charge, defect complexes, and microstructure are assumed to be responsible for the change in the dielectric constant and the relaxation mechanism. [ABSTRACT FROM AUTHOR]

A series of TaC/SiC multilayer films with different SiC thicknesses (t SiC ) have been prepared by magnetron sputtering and their microstructure, hardness and toughness investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning electron microscopy (SEM) and nanoindentation. Results show that SiC crystallized and grew coherently with TaC layers at low t SiC (≤ 0.8 nm), resulting from the template effect of TaC layers. Maximum hardness and toughness of 46.06 GPa and 4.21 MPa m 1/2 were achieved at t SiC = 0.8 nm with good coherent interface. With further increasing of t SiC , SiC layers partially transformed to an amorphous structure and gradually lost their coherent interface, leading to a rapid drop in hardness and toughness. The crystallization of SiC layers and the coherent growth are required to achieve superhardness and high toughness in the TaC/SiC multilayers. [ABSTRACT FROM AUTHOR]

Transition metal nitrides are being widely applied, as durable sensors, semiconductor and superconductor devices, their electrical conductivity and wear resistance having a significant influence on these applications. However, there are few reports about how to improve above properties. In this paper, tantalum was incorporated into hafnium nitride films through Hf 1- x Ta x N y [ x =Ta/(Hf+Ta), y =N/(Hf+Ta)] solid solution. The electrical conductivity and wear resistance of the films were significantly improved, due to the increase of the electron concentration (tantalum has one more valence electron than hafnium) and the increase in H/E and H 3 /E 2 ratios caused by the effect of solid solution hardening, respectively. The highest electrical conductivity of Hf 1- x Ta x N y films is 8.3×10 5 S m −1 , which is 1.7 times and 5.2 times of that of hafnium nitride and tantalum nitride films, respectively. In addition, the lowest wear rate of films is 1.2×10 −6 mm 3 /N m, which is only 10% and 48% of that of hafnium nitride and tantalum nitride films, respectively. These results indicate that alloying with another transition metal is an effective method to improve electrical conductivity and wear resistance of transition metal nitrides. [ABSTRACT FROM AUTHOR]