The elastic constant tensor of an inorganic compound provides a complete description of the response of the material to external stresses in the elastic limit. It thus provides fundamental insight into the nature of the bonding in the material, and it is known to correlate with many mechanical properties. Despite the importance of the elastic constant tensor, it has been measured for a very small fraction of all known inorganic compounds, a situation that limits the ability of materials scientists to develop new materials with targeted mechanical responses. To address this deficiency, we present here the largest database of calculated elastic properties for inorganic compounds to date. The database currently contains full elastic information for 1,181 inorganic compounds, and this number is growing steadily. The methods used to develop the database are described, as are results of tests that establish the accuracy of the data. In addition, we document the database format and describe the different ways it can be accessed and analyzed in efforts related to materials discovery and design.

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Charting the complete elastic properties of inorganic crystalline compounds

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Ab initio study of MnO and NiO

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Charting the complete elastic properties of inorganic crystalline

We examine the performance of hybrid (HF-DFT) exchange functionals within Density Functional Theory (DFT) in describing the properties of crystalline solids. Recent applications are reviewed, and an extensive set of new results presented on transition metal compounds.

The Performance of Hybrid Density Functionals in Solid State Chemistry

The Impulse Excitation Technique (IET) was used to determine the elastic modulus and specific damping of different Ni/NiO–YSZ composites suitable for use in solid oxide fuel cells (SOFC). The porosity of the as-sintered samples varied from 9 to 38% and that of the reduced ones from 31 to 52%. For all samples a linear relation between Young's modulus and porosity was found. The temperature dependency of the mechanical properties of both as-sintered and reduced composites was investigated by IET up to 1200 °C. In the as-sintered state, first an increase and peak of stiffness coinciding with the Neel temperature, 250 °C, of NiO was observed. Above this temperature, a linear decrease occurred. Specific damping showed a peak at 170–180 °C and increased above ca. 1000 °C in NiO–YSZ. In the reduced state the elastic modulus decreased linearly with temperature; specific damping increased above ca. 600 °C and was found to be very dependent on microstructure. Damage caused by redox cycling degraded the elastic properties of the composites. Degradation started linearly from 0.5 to 0.6% redox strain leading to macroscopic sample failures at about 2.5% dL/L o . A simple continuum elastic damage model was fitted to the degradation data.

Mechanical properties of NiO/Ni–YSZ composites depending on temperature, porosity and redox cycling

The elastic constants of a single crystal of NiO are determined by an ultrasonic measuring technique. Near the Neel temperature clearly defined anomalies are observed in 1/2 (C11-C12) and 1/2(C11+C12+2C44) but not in C44. These results are discussed in terms of the thermodynamic theory for second order phase transitions and the necessity for further measurements are emphasized.

https://iopscience.iop.org/article/10.1088/0022-3719/4/14/013/pdf

Elastic constants of a NiO single crystal: I (Magnetic transitions)

For Pt. I see ibid., vol.4, 1983 (1971). Magnetostriction measurements along the (110) and (112)axes of a NiO single crystal, which was compressed along the (111) direction in order to produce a twin free specimen, are reported. At fields up to 10-15 kOe the strain varies with H2 and this is interpreted as due to the movement of spin domains. At higher fields a tendency towards saturation is found. The ordinary anisotropic magnetostriction was measured along the (110) and (112) axes by rotation of an applied field of 25 kOe in the (111) plane to the perpendicular directions. The temperature dependence of the resulting strain -1/3(A1+A2+2/3A4+1/6A5), as described in terms of the equation of Birss (1959), is given and it takes values of 33*10-6 and 23*10-6 at room temperature as measured along respectively the (110) and (112) axes. An attempt towards comparison with the single ion theory of Callen and Callen (1963) was made, but this was hindered by the large temperature dependence of the elastic constants of NiO. The temperature dependence of the forced exchange magnetostriction in the (111) plane, which shows a discontinuity at the Neel point and which persists with a large and remaining constant value in the paramagnetic region, is also given.

http://iopscience.iop.org/article/10.1088/0022-3719/4/16/021/pdf

S. J. van Tonder

Papers

Elastic constants of a NiO single crystal: I (Magnetic transitions)

Magnetostriction of a NiO single crystal. II