Synthesis and characterization of polycrystalline KAlSi3O8 hollandite [liebermannite]: Sound velocities vs. pressure to 13 GPa at room temperature

A polycrystalline specimen of liebermannite [KAlSi₃O₈ hollandite] was synthesized at 14.5 GPa and 1473 K using glass starting material in a uniaxial split-sphere apparatus. The recovered specimen is pure tetragonal hollandite [SG: I4/m] with bulk density of within 98% of the measured X-ray value. The specimen was also characterized by Raman spectroscopy and nuclear magnetic resonance spectroscopy. Sound velocities in this specimen were measured by ultrasonic interferometry to 13 GPa at room T in a uniaxial split-cylinder apparatus using Al₂O₃ as a pressure marker. Finite strain analysis of the ultrasonic data yielded K_S0 = 145(1) GPa, K₀′ = 4.9(2), G₀ = 92.3(3) GPa, G₀′ = 1.6(1) for the bulk and shear moduli and their pressure derivatives, corresponding to V_P0 = 8.4(1) km/s, V_S0 = 4.9(1) km/s for the sound wave velocities at room temperature. These elasticity data are compared to literature values obtained from static compression experiments and theoretical density functional calculations.