Electrical resistivity and Hall effect in sodium tungsten bronze
The electrical resistivity and Hall coefficient of sodium tungsten bronze have been measured as a function of sodium concentration and temperature. Measurements were on single crystals with values of x between 0.58 and 0.90, where x is the x in NaxWO3;The room temperature resistivity possessed a minimum value of (3.20 +/- 0.14) x 10-5 ohm-cm. at x = 0.75 in agreement with previously reported results. The resistivity was (12.5 +/- 0.23) x 10-5 ohm-cm. at x = 0.584 and (5.89 +/- 0.20) x 10-5 ohm-cm. at x = 0.863;The resistivity was linear with temperature in the range 125°K. to 300°K. The temperature coefficient of resistivity was also a minimum at x = 0.75. The value of the temperature coefficient of resistivity at that concentration was (9.45 +/- 0.60) x 10-8 ohm-cm./°C. The residual resistivity was obtained by extrapolation of the resistivity to absolute zero. The residual resistivity was a minimum at x = 0.75 with a value of (1.25 +/- 0.10) x 10-5 ohm-cm;The Hall coefficient varied less than 2 percent with temperature in the range 78°K. to 370°K. The Hall coefficient was inversely proportional to the sodium concentration, varying from -(6.10 +/- 0.15) x 10-4 cm.3/coulomb at x = 0.584 to -(4.07 +/- 0.03) x 10-4 cm.3/coulomb at x = 0.897. The values for the Hall coefficient corresponded very nearly to one free electron for each sodium atom;The minimum in the curve of resistivity as a function of sodium concentration is due to an anomalous maximum in the electron mobility at x = 0.75. The reasons for this anomaly are not clearly understood.