Metal–Insulator Transition in BixV₈O₁₆:⁵¹V NMR Study

The 51 V nuclear magnetic resonance and relaxation (NMR) are measured for Bi x V 8 O 16 in the temperature range from 4.2 K to 280 K. The Bi x V 8 O 16 system with 1.60 ≤ x ≤1.80 is known to crystallize in the Hollandite structure with a [V 8 O 16 ] framework which is composed of double chains formed by edge-shared VO 6 octahedra. In this system, we observed temperature-induced Metal–Insulator transition (MIT) in the composition range of 1.72 ≤ x ≤1.80. In order to reveal the mechanism of MIT in this system, 51 V NMR measurements have been performed on Bi 1.77 V 8 O 16 as well as on the simple Pauli paramagnetic compound Bi 1.60 V 8 O 16 for a comparative study: the Knight shift K and the spin–lattice relaxation rate 1/ T 1 of 51 V NMR have been measured to investigate the magnetic and electric properties. By applying the random phase approximation (RPA) method the absolute values of 1/ T 1 T are analyzed in the Pauli paramagnetic regime of Bi 1.77 V 8 O 16 above T MIT and Bi 1.60 V 8 O 16 for whole temperature region. As a result, the modification factor K (α) for applying the RPA theory to the interacting system has been found to be 0.9 (nearly non-interacting) for the case of x =1.60 and 1.7 (antiferromagnetic) for x =1.77, implying that the antiferromagnetic spin correlation and frustration may cause the occurrence of MIT in Bi 1.77 V 8 O 16 .