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The Knoop hardness of the highly incompressible cubic phase of ruthenium dioxide was found to be 19–20 GPa from indentation tests. This value scales well with the shear modulus approximated by the elastic constant C[sub 44] of 144 GPa obtained from Brillouin scattering measurements. This work provides evidence that the shear modulus is a better indicator of hardness than the bulk modulus for ionic and covalent materials. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Behaviour of magnetic excitations in the Damon–Eshbach (DE) and backward volume (BV) geometries in nano-composite (SiO2)100− x Co x (50%at

Germanium nitride, having cubic spinel structure, γ-Ge 3 N 4 , is a wide band-gap semiconductor with a large exciton binding energy that exhibits high hardness, elastic moduli and elevated thermal stability up to approximately 700°C. Experimental data on its bulk and shear moduli ( B 0 and G 0 , respectively) are strongly limited, inconsistent and, thus, require verification. Moreover, earlier first-principles density functional calculations provided significantly scattering B 0 values but consistently predicted G 0 much higher than the so far available experimental value. Here, we examined the elasticity of polycrystalline γ-Ge 3 N 4 , densified applying high pressures and temperatures, using the techniques of laser ultrasonics (LU) and Brillouin light scattering (BLS) and compared with our extended first-principles calculations. From the LU measurements, we obtained its longitudinal- and Rayleigh wave sound velocities and, taking into account the sample porosity, derived B 0  = 322(44) GPa and G 0  = 188(7) GPa for the dense polycrystalline γ-Ge 3 N 4 . While our calculations underestimated B 0 by approximately 17%, most of the predicted G 0 matched well with our experimental value. Combining the LU- and BLS data and taking into account the elastic anisotropy, we determined the refractive index of γ-Ge 3 N 4 in the visible range of light to be n  = 2.4, similarly high as that of diamond or GaN, and matching our calculated value. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'.

In order to get better knowledge of mechanical properties from microscopic to macroscopic scale of biopolymers, viscoelastic bulk properties of aqueous solutions of sodium alginate were studied at different scales by combining macroscopic shear rheology (Hz), diffusing-wave spectroscopy microrheology (kHz-MHz) and Brillouin spectroscopy (GHz). Structural properties were also directly probed by small-angle X-ray scattering (SAXS). The results demonstrate a change from polyelectrolyte behavior to neutral polymer behavior by increasing polymer concentration with the determination of characteristic sizes (persistence length, correlation length). The viscoelastic properties probed at the phonon wavelength much higher than the ones obtained at low frequency reflect the variation of microscopic viscosity. First experiments obtained by metabolic activity assays with mouse embryonic fibroblasts showed biocompatibility of sodium alginate aqueous solutions in the studied range of concentrations (2.5-10 g L -1 ) and consequently their potential biomedical applications.

These data are supplied for supporting their interpretations and discussions provided in the research article "Large influence of vacancies on the elastic constants of cubic epitaxial tantalum nitride layers grown by reactive magnetron sputtering" by Abadias et al. (2020) [doi: 10.1016/j.actamat.2019.11.041]. The datasheet describes the experimental methods used to measure the longitudinal (V L ) and transverse (V T ) sound velocities of cubic epitaxial TaN/MgO thin films, and their related cubic elastic constants (c 11 , c 12 and c 44 ), by the picosecond laser ultrasonic (PLU) and the Brillouin light scattering (BLS) techniques, respectively. First-principles numerical simulations provide additional data using specifically designed supercells of TaN structures, generated either by hand or using the alloy theoretical automated toolkit (ATAT) method [A. Zunger et al. (1990)], with different configurations (random, cluster and ordered) of defects (Ta and N vacancies). Phonons calculations support discussion of dynamical mechanical stability of defected TaN cubic structures. The data illustrate the huge role of vacancies in elastic properties and phase stability of TaN films., (© 2020 The Author(s).)