14N NQR and phase transitions in tetracyanoquinodimethanide alkaline salts

Abstract

14N NQR lines of RbTCNQ and NaTCNQ polycrystalline samples, measured as a function of temperature, show small but sharp discontinuities at the regular-alternant phase transition (found respectively at 214 K and 346 K), together with the expected change in spectral multiplicity. No ν − lines were detected in NaTCNQ. Co-existence of phases, more marked in NaTCNQ, shows up in NQR data. The use of a pulsed, FT spectrometer yields estimates of T 1 relaxation time: it shows no discontinuity at the phase transition, is around 1 ms at room temperature for ν+ lines, more than 2 order of magnitudes larger for ν − lines, increases smoothly on decreasing temperature.