Bulk modulus of osmium, 4-300 K

We determined osmium's 0-300 K monocrystal and polycrystal bulk modulus using two ultrasonic methods: resonant ultrasound spectroscopy and a novel pulse-echo method. All other recent bulk modulus measurements on osmium have used high-pressure X-ray diffraction, a method with known lower accuracy than ultrasonic methods. Our study was motivated by current theoretical and measurement disputes over osmium's bulk modulus and whether it exceeds that of diamond. At all temperatures, we found osmium's bulk modulus to be much lower (by 7-8%) than diamond's. The room-temperature bulk modulus for osmium is 405 GPa; extrapolation to 0 K gives 410 GPa. Osmium's 0-300 K bulk modulus change is unusually small: about 1%. Temperature behavior is smooth, fitting closely to an Einstein-oscillator model.