Electrical properties of NbO2 and Nb2O5 at elevated temperature in air and flowing argon
Abstract
NbO2, heated in air, shows sharply decreasing electrical resistance until oxidation occurs at about 486°C and forms L-Nb2O5. This oxidation is accompanied by a first-order increase in electrical resistance. Further heating causes only a slight decrease in resistance until the occurrence of a minimum resistance anomaly, centered at about 800°C, and showing for the most part a second-order character of the singularity type. The magnitude of this effect is considerably larger in the cooling direction, and the recovered product gives the x-ray pattern of L-Nb2O5 rather than the high-temperature H phase of Nb2O5. Heating the sample under flowing argon postponed the reaction to Nb2O5 to about 750°C however, in the cooling direction, the reversal of the anomaly near 800°C is clearly observed. The minimum resistance anomaly is interpreted to arise from an intermediate stage of a phase transformation centered about reduction and reoxidation phenomena. Heating β-Nb2O5 in flowing argon causes a reversible first-order decrease in resistance beginning at about 450°C associated with the β-->δ phase transformation followed by a minimum in resistance at 700-1000°C interpreted as above. In the cooling direction the minimum in resistance occurs between 900 and 700°C, and the recovered product gives the x-ray pattern of Nb2O5 (105M) which is a structure very similar to the H phase.
- Publication:
-
Physical Review B
- Pub Date:
- October 1982
- DOI:
- 10.1103/PhysRevB.26.3954
- Bibcode:
- 1982PhRvB..26.3954V