Thermoelastic properties of non-metamict zircon

The thermoelastic properties and thermal expansion of natural single-crystal zircon without detectable radiation damage were determined in the temperature range between 100 and 1650 K on five samples from Cambodia, Sri Lanka, and Tanzania. Up to about 1500 K, the results are in excellent agreement and fully reversible. The average adiabatic elastic stiffness coefficients at room temperature in GPa are c(11) = 426.8(6), c(12) = 68.1(4), c(13) = 152.0(4), c(33) = 490.8(9), c(44) = 113.1(2), and c(66) = 49.0(1). Polycrystalline averaging for the aggregate bulk and shear modulus (Voigt-Reuss-Hill average) yields K = 229.3(4) GPa and G = 109.3(1) GPa. From 293 to 1573 K, the elastic stiffnesses soften almost linearly with the temperature coefficients in MPa/K: dc(11)/dT = -45.36(7), dc(12)/dT = -2.03(7), dc(13)/dT= -9.59(7), dc(33)/dT = -42.85(12), dc(44)/dT = -9.60(3), and dc(66)/dT = -2.19(1). Below room temperature, the behavior of the c(ij) is nonlinear, with decreasing absolute values of the temperature coefficients. Above about 1500 K, a temperature- and time-dependent irreversible elastic stiffening accompanied by an increasing ultrasound dissipation was observed in all samples. These anomalies are interpreted to be the consequence of increased dislocation densities.