ELECTRONIC SPECIFIC HEAT OF SODIUM TUNGSTEN BRONZE

The design and operation of a calorimeter for use in the temperature range 1.8 to 4.2 deg K are presented, and the methods used in the treatment of data and calculation of results are discussed. The heat capacities of several Na- W bronzes (Na/sub x/WO/sub 3/) were determined in the temperature interval 1.8 to 4.2 deg K. Samples having x equal to 0.89, heat capacities are described adequately by the sum of two terms, one linear and one cubic in temperature. The electronic specific heat of each sample is obtained by evaluating the coefficient of the linear term, and the Rebye eharacteristic temperature derived from the coefficient of the cubic term. Rensities of one-electron energy levels at the Fermi energy, and effective electronic masses are calculated from the electronic specific heats. A plot of the density of states as a function of energy can be made if it is assumed that this curve is independent of Na concentration. The justification of this assumption is discussed in the light of current theories of the solid state. The density of states curve rises rapidly at higher energies, and this rise is interpreted in terms of the filling of a Brillouin zone ormore » of an overlap of two bands. (auth)« less