Thermoelastic properties of natural zircon – Part I: Non-metamict zircon

9 The thermoelastic properties and thermal expansion of natural single-crystal zircon without detectable 10 radiation damage were determined in the temperature range between 100 K and 1650 K on five 11 samples from Cambodia, Sri Lanka, and Tanzania. Up to about 1500 K, the results are in excellent 12 agreement and fully reversible. The average adiabatic elastic stiffness coefficients at room temperature 13 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). 14 Polycrystalline averaging for the aggregate bulk and shear modulus (Voigt-Reuss-Hill average) yield K 15 = 229.3(4) GPa and G = 109.3(1) GPa. From 293 K to 1573 K, the elastic stiffnesses soften almost 16 linearly with the temperature coefficients in MPa/K: d c 11 /d T = -45.36(7), d c 12 /d T = -2.03(7), d c 13 /d T = - 17 9.59(7), d c 33 /d T = -42.85(12), d c 44 /d T = -9.60(3), and d c 66 /d T = -2.19(1). Below room temperature, the 18 behavior of the c ij is non-linear, with decreasing absolute values of the temperature coefficients. Above 19 about 1500 K, a temperature-and time-dependent irreversible elastic stiffening accompanied by an 20 increasing ultrasound dissipation was observed in all samples. These anomalies are interpreted to be the 21 consequence of increased dislocation densities.