Self-diffusion of boron in TiB2

Abstract

Self-diffusion studies of boron in polycrystalline TiB2 were carried out as a function of temperature, using a specially designed experiment with stable B10 tracers, B−enriched11 TiB2 samples, and secondary ion mass spectrometry for depth profiling. The diffusivities were extracted from the isotope depth profiles in the range between 950 and 1600 °C. They obey an Arrhenius behavior with an activation enthalpy of about ΔH=2.2 eV and a preexponential factor of D0=4×10−12 m2/s. Interpolation of the diffusivities to the melting point of 3225 °C reveals a very low value of about D(Tm)≈10−15 m2/s, which reflects the covalent bonds present in the material. A possible explanation for the low values obtained for D0 and ΔH is the assumption of a diffusion mechanism via vacancies, where in addition to thermal vacancies a substantial concentration of structural vacancies are present. The possible influence of grain boundaries and of the anisotropic crystal structure on the results is discussed together with crystallographic diffusion paths.

Slow Lithium Transport in Metal Oxides on the Nanoscale

“…A well suited technique of tracer deposition in lithium containing solids is the use of isotope heterostructures [30][31][32][33]. There, on top of a bulk crystal or a thin film of a material with natural isotope composition under investigation Li x A (A: arbitrary species or combination of species; x: relative lithium fraction), a material of identical or almost identical chemical composition is deposited, which, however, is enriched with 6 Li.…”

Lithium Diffusion in Ion-Beam Sputtered Amorphous LiAlO2

“…In the present study we used 6 LiAlO 2 / 7 LiAlO 2 isotope hetero-structures for analysis. This is a reliable method to study self-diffusion processes in solids because pure isotope interdiffusion takes place undisturbed by chemical gradients [17][18][19][20][21][22].…”

Improving Hardness and Toughness of Boride Composites Based on AIMgB₁₄

“…Diffusion studies of B isotopes in TiB 2 have shown it to have low self-diffusivity of B atoms, even when near its melting temperature of 3225ºC [58]. This is evidence of the strong covalent bonds present and explains the difficulty of sintering this material.…”

“…In fact, the electrical conductivity of Ti metal is lower than that of its diboride [55][56]. Some of these, especially TiB 2 , also have considerable resistance to various forms of corrosion including attack from oxidation, liquid metals, and acids [55,[57][58]. Since these diborides have the same crystal structure, many of these compounds also have complete solid solubility with each other [54,[59][60].…”