KAUST Repository

Topaz is an aluminosilicate mineral phase stable in the hydrothermally altered pegmatitic rocks and also in subducted sedimentary lithologies. In nature, topaz often exhibits solid solution between fluorine and hydrous end members. We investigated elasticity of naturally occurring single crystal topaz (Al2SiO4F1.42(OH)0.58) using Resonant Ultrasound Spectroscopy. We also explored the temperature dependence of the full elastic constant tensor. We find that among the various minerals stable in the Al2O3-SiO2-H2O ternary system, topaz exhibits moderate elastic anisotropy. As a function of temperature, the sound velocity of topaz decreases with and being −3.10 and −2.30 × 10−4 km/s/K. The elasticity and sound velocity of topaz also vary as a function of OH and F content. The effect of composition () on the velocity is equally important as that of the effect of temperature. We also note that the Debye temperature () of topaz at room temperature condition is 910 K and decreases at higher temperature. The Debye temperature shows positive correlation with density of the mineral phases in the Al2O3-SiO2-H2O ternary system.

Relaxor ferroelectric materials, such as PMN-PT with generic stoichiometry Pb[(Mg 0.33 Nb 0.67) 1-x Ti x ]O 3 undergo a ferroelectric to paraelectric phase transition as a function of temperature. The exact transition characterized by Curie temperature () varies as a function of chemistry (), i.e., the concentration of Ti. In this study, we investigated the structural phase transition by exploring the temperature dependence of the single crystal elastic properties of Pb[(Mg 0.33 Nb 0.67) 0.7 Ti 0.3 ]O 3 i.e., 0.3. We used resonant ultrasound spectroscopy (RUS) to determine the elasticity at elevated temperatures, from which a 398 5 for PMN-PT (0.3) was determined. We report the full elastic constant tensor (, , }), acoustic attenuation (), longitudinal (), and shear () sound velocities, and elastic anisotropy of PMN-PT as a function of temperature for 400 871 K. Temperature trends of the elastic constants , and bulk modulus indicate that at the material first stiffens and reaches maxima in the vicinity of the Burns temperature (~673 K), followed by a more typical gradual softening of the elastic constants. Similar temperature dependent anomalies are also observed with anisotropy and , with minima in the vicinity. We used the temperature dependence of , , , , and anisotropy to infer the evolution of polar nanoregions (PNRs) as the material evolved from .

Because of health and environmental concerns about lead, lead-free solder alloys in most consumer electronics have been required in the European Union since 2006. Many of these alloys are prone to mechanical failure over time, leading to less reliable circuitry. The source of these failures is not well known and many have conjectured that the coarse grained alloys become more brittle over time when exposed to elevated temperatures (~100 °C). Our group, in collaboration with Cisco Systems, has recently studied the effects of aging on the mechanical properties of Sn-Ag-Cu (SAC) solder alloys using using both resonant ultrasound spectroscopy (RUS) and conventional pulse-echo methods. With grain sizes on the order of 100's of microns, the heterogeneity of these alloys present a particular problem for RUS and interpretation of pulse-echo data. Resonance data exhibiting the effect of the heterogeneity will be presented and discussed. Elastic moduli derived from pulse-echo methods as a function of temperature and isothermal aging time will also be shown.

Elasticity of mineral phases at temperature and pressure conditions relevant to earth interior is essential for constraining the composition and the dynamics of the deep Earth. To constrain the temperature dependence of elasticity of hydrous minerals relevant to the earth’s subduction zones, we used high temperature Resonance Ultrasound Spectroscopy (RUS). We explored the temperature dependence of the full elastic moduli tensor, speed of sound, attenuation, and anisotropy of naturally occurring single crystal topaz (Al2SiO4F1.42(OH)0.58) [1] with a rectangular parallelepiped geometry. The RUS spectra are influenced by the geometry, density, and the full elastic moduli tensor [2]. We determined the crystal symmetry and crystallographic alignment of the crystals using X-ray diffraction. The geometry and density are well constrained from previous results on thermal expansion. The elasticity results on topaz are in good agreement with previous studies. We combine the high temperature elasticity of natural topaz with the results from the first principles on end member hydrous topaz and shed insight into how pressure temperature and composition, i.e., the fluorine and hydrogen content could influence elasticity of minerals in the Earth’s interior, in particular in subduction zone settings. [Work supported by U.S. NSF Award Nos. EAR-1634422 and EAR-1753125.] References: [1] Tennakoon et al., Sci. Rep., 8, 1372 (2018). [2] A. Migliori and J. D. Maynard, Rev. Sci. Instrum.76, 121301 (2005).

Lead magnesium niobate—lead titanate (PMN-PT) exhibits exceptional electromechanical properties, considered as a highly efficient transduction material for vibration energy harvesting and acoustic sensing applications. It is reported in the literature that the PMN-PT undergoes structural phase transitions with changes in temperature and the chemical composition. We seek to gain insight into the phase diagram of PMN-PT using temperature and pressure dependence of the elastic properties. Single crystal PMN-PT with chemical composition close to the morphotropic phase boundary (MPB) was used in a resonant ultrasound spectroscopy (RUS) study performed in the temperature range from room temperature to 773 K and the pressure range from near vacuum to 3.4 MPa. At atmospheric pressure, significantly high acoustic attenuation of the PMN-PT material is observed at the temperatures below 400 K. Strong stiffening is observed in the temperature range of 400 K–673 K, followed by a gradual softening at higher temperatures. With the varying pressure, we observed an increased pressure sensitivity of elastic properties of the PMN-PT material that can be localized to the temperature regime where the strong stiffening is observed. As time allows, the behavior of PMN-PT upon cooling below room temperature will also be discussed.

Lead magnesium niobate-lead titanate [(1-x)PbMg1/3Nb2/3O3-xPbTiO3] is a perovskite relaxor ferroelectric material exhibiting superior electromechanical coupling compared to the conventional piezoelectric materials. In this work, non-poled single crystal PMN-PT material with the composition near morphotropic phase boundary (MPB) was investigated in the temperature range of 400 K—800 K where the material is reported to be in the cubic phase. High temperature resonant ultrasound spectroscopy (HT-RUS) technique was used to probe temperature dependency of elastic constants derived from the measured resonant modes. Non-monotonic resonant frequency trends in the temperature regime indicate stiffening of the material, followed by gradual softening typically observed in heated materials. Elastic constants confirmed this stiffening in the temperature range of 400 K—673 K, where the stiffness constants C11 and C44 increased approximately by 40% and 33% respectively. Acoustic attenuation, derived from the quality factor (Q), exhibits a minimum around the temperature where the stiffness is maximum and, significantly higher attenuation observed at temperatures below 400 K. The temperature range 395 K—405 K was identified as a transition temperature range, where the material showed an abrupt change in the resonant spectrum and, the material emerges from the MPB characterized by this very high acoustic attenuation. This transition temperature compares favorably with dielectric constant measurements reported in the literature.

Temperature dependence of the elastic constants of polycrystalline rare-earth doped strontium titanate (STO) [ Sr0.9X0.1TiO3-δ (X = Pr, Y)] was investigated in the temperature range of 300 K—750 K using resonant ultrasound spectroscopy. Elastic constants of undoped STO decrease linearly indicating typical softening with increased temperature. Yttrium (Y) doped STO also exhibits a monotonic softening, however, with a pronounced curvature in this high temperature regime. Trends of elastic constants of the praseodymium (Pr) doped STO show a non-monotonic stiffing from room temperature to 475 K, followed by a gradual softening. Changes in attenuation were quantified by the inverse quality factor (1/Q) averaged over measured resonances. Undoped STO showed a monotonic gradual increase of attenuation with increasing temperature while yttrium doped STO showed little variation. In contrast, attenuation of Pr doped STO exhibited a peak around 425 K. These results will be compared to thermal conductivity measurements in the same temperature range and phonon scattering mechanisms will be discussed.