Nanoindentation and ellipsometry of Li2ZnTi3O8 & Zn2TiO4 single crystals
Publikation aus Materials
Perfler L., Kahlenberg V., Wikete C., Priv. Doz. Mag. Dr. Reinhard Kaindl
Acta Crystallographica Section A, 70, (a1), C1116 , 8/2014
Spinel-type Li2ZnTi3O8 and Zn2TiO4 are useful for various industrial applications due to their interesting chemical and physical properties, for example, as promising anode materials in Li-ion batteries or as components in dielectric devices . Since Li2ZnTi3O8 and Zn2TiO4 are expected to have high refractive indices (n calc. = 2,33 and 2,26) we tried to characterize these materials in more detail including single-crystal X-ray diffraction, nanoindentation, spectroscopic ellipsometry and electron microprobe analysis. Single crystals of Li2ZnTi3O8 and Zn2TiO4 were grown directly from melt at 1723 K and 1873 K, respectively. Fragments of sintered polycrystalline Li2ZnTi3O8 and Zn2TiO4 precursors were placed on an iridium sheet and fired in a muffle furnace from 1273 to 1723/1873 K with a heating ramp of 15 K/min. After a dwell time of 3 min the melt was cooled down to 1473 K with a ramp of 10 K/min and subsequently quenched in water. Structural investigations of the Li2ZnTi3O8 and Zn2TiO4 single crystals resulted in the following basic crystallographic data: cubic, P4332, a = 8.3697(2) Å, V = 586.31(3) Å3, Z = 4 and Fd-3m, a = 8.46230(17) Å, V = 605.99(2) Å3, Z = 8, respectively. Nanoindentation experiments were performed with a Berkovich diamond indenter tip to determine the hardness and elastic modulus of Zn2TiO4 and Li2ZnTi3O8. For sample preparation the single crystals were embedded in resin and polished to a mirror-like surface finish. More than 150 indents with a distance of 10 µm were made with a maximum load of 20 mN. Analysis of the load-displacement curves for Zn2TiO4 revealed a hardness of 10.51 1 0.39 GPa and a reduced elastic modulus of 180.90 1 3.92 GPa. Atomic force micrographs displayed indents with a max. depth of 288 1 5 nm. Li2ZnTi3O8 exhibited a hardness of 6.86 1 0.45 GPa and a reduced elastic modulus of 148.88 1 6 GPa. Zn2TiO4 showed a dispersion of 0.09 due to the variation of the refractive index from 2.24 (430,8 nm, Fraunhofer G line) and 2.15 (686,7 nm, B line).