Electrical resistivity and Hall effect in the mixed system Ti1-xHfxSe2

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Abstract
Electrical properties of single crystals of Ti1-xHfxSe2 (0<or=x<or=0.5) are studied at temperatures between 20 and 290K. The nature of the conduction is metallic for the range of x investigated except for a resistivity anomaly. The resistivity anomaly associated with a phase transition appears when 0<or=x<0.4. The sign of the Hall coefficient at room temperature is positive for 0<or=xor=0.4 where the transition is completely suppressed. The results show that the presence of holes is essential to the occurrence of the phase transition. Furthermore, a characteristic change is found in the temperature dependence of the Hall coefficient as x is increased. This feature is similar to the contrasting temperature dependence of Hall coefficient between a pure and impure system which is predicted for an excitonic insulator.