Elastic constants of NbO2at room temperature

Measurements have been made of the transit times of pulses of longitudinal and transverse ultrasonic waves propagating in single-crystal Nb${\mathrm{O}}_2$ at room temperature. A unique set of values for the seven independent elastic constants of the semiconducting, distorted-rutile-structure phase of Nb${\mathrm{O}}_2$ has been calculated from the resultant velocities using a novel algebraic technique. A room-temperature elastic Debye temperature of 591 ± 6 K is found. Its value is very close to the calorimetric Debye temperature deduced from low-temperature heat-capacity data by one investigater but significantly larger than that found by another group. No definite evidence has been found yet for phononlike excitations of charge-density waves from comparison of our ultrasonic results with the calorimetric data of others.