The compressional and shear wave velocities in a series of polycrystal samples of magnesiowustite (Mgx, Fe1‐x)YO have been measured using the pulse superposition method. Each specimen was characterized in terms of composition, stoichiometry, and porosity by chemical and microprobe analysis, and by X ray diffraction. In addition, the measurement of velocity in three perpendicular directions has demonstrated that the individual specimens were isotropic to within 1/4%. The application of empirical corrections to account for the effects of nonstoichiometry and porosity has allowed the determination of the isotropic elastic properties for the entire stoichiometric (Mg,Fe)O solid solution series. Our results for MgO (KS = 1619 ± 16 kbar, μ = 1304 ± 16 kbar) are consistent with previous determinations of these properties from single‐crystal measurements. In the case of FeO (KS = 1835 ± 31 kbar, μ = 589 ± 14 kbar), our data generally correspond to the results of previous investigations, which used both ultrasonic and static compression techniques, when corrections are applied for the effects of nonstoichiometry. Our measurements on Fe‐rich magnesiowustites have demonstrated clearly that the isotropic elastic properties, especially the bulk modulus KS, are strongly dependent on the defect structure (nonstoichiometry) of the specimens. The increasing number of vacancy clusters toward the FeYO end‐member correlates with decreasing bulk modulus and anomalously high values of (∂K /∂P)T. However, when corrections are applied for the nonstoichiometric effects, the elastic properties of the (Mg, Fe)O solid solution series behave according to the linear compliance relation proposed by Liu (1968) and Jackson et al. (1978).

This paper reports the ultrasonic measurements of the single‐crystal second‐order elastic constants and their pressure and temperature derivatives for a natural sample of pyrope garnet of composition (Mg0.61, Fe0.36, Ca0.02)3Al2Si3O12. Within the experimental precision of the pulse superposition method the pressure and temperature dependences of each of the three independent elastic constants were found to be linear in the range up to 10 kbar and from ambient conditions to 100°C. The pertinent results for the adiabatic bulk modulus are K0s = 1682.1 ± 3.6 kbar, (∂Ks/∂P)T = 4.74 ± 0.16, and (∂Ks/∂T)P = −0.188 ± 0.006 kbar/°C, where each parameter is evaluated at 1 bar and 25°C. These results are generally consistent with previous studies of the elasticity of pyrope garnet using high‐pressure static compression methods; however, the present data have the advantage of increased precision and accuracy. In addition, comparison of our results with corresponding data for other (Mg, Fe, Mn, Ca)3Al2Si3O12 garnets suggests that the specific type of the divalent cation in the eightfold coordination site has a relatively minor effect on the elastic properties of garnet, except for the Ca‐rich end‐member, grossularite.

The second order elastic constants of unpoled ferroelectric lead germanate, Pb5Ge3O11, have been measured from 25 to 240 °C by using the ultrasonic pulse superposition method. The elastic moduli c11, c33, c12, and c13 show downward directed cusp‐like anomalies near the ferroelectric Curie temperature at 177 °C, but the shear moduli c44 and c66 show only a small and monotonical decrease with temperature. For c33 and c13 the correction for piezoelectric stiffening is large and increases the magnitude of the elastic anomaly. By separating the elastic constants into a linearly temperature dependent part c μitalicv0 and the elastic anomaly Δcμv it is found that for the ferroelectric phase the anomalous contributions of the unstiffened constants obey the relations Δc11 = Δc12 and Δc11Δc33 = (Δc13)2. A group theoretical analysis shows that these relations follow if the soft Raman mode of A symmetry dominates the internal strain contributions to the elastic constants. This suggests that the elastic anomaly is predominantly caused by the linear acoustic–optic mode interaction proposed by Miller and Axe for the elastic anomaly in β‐quartz.

The single-crystal elastic constants, their temperature coefficients, and the thermal expansion coefficients of natrual nepheline, (KAlSiO4)(NaAlSiO4)3, have been measured. The longitudinal modulus c11 and the shear modulus c66 have positive temperature coefficients. Since this implies the existence of a wide range of directions with a zero temperature coefficient of the ultrasonic travel time, nepheline may be a suitable substrate for ultrasonic surface-wave signal processing devices.