Nuclear Quadrupole Effect and Phase Transition in the Quasi‐One‐Dimensional Conductor β‐Na0.33 V2O5

The angular dependence of the main NMR resonance lines of the 51V nuclei in β‐Na0.33V2O5 is measured above and below the first‐order structural phase transition temperature in the frequency range between 10 and 20 MHz. The nuclear quadrupole interaction parameters of the broad resonance line are determined, and the principal axes of the electric field gradient tensor are found to coincide with those of the crystalline field around the vanadium atoms in site I.