We measured X-band electron-spin resonance of single-crystalline sodium vanadate doped with lithium ${\mathrm{Na}}_{1-x}{\mathrm{Li}}_x{\mathrm{V}}_2{\mathrm{O}}_5$ for $0<~x<~1.3\%.$ The phase transition into a dimerized phase that is observed at 34 K in the undoped compound, was found to be strongly suppressed upon doping with lithium. The spin susceptibility was analyzed to determine the transition temperature and the energy gap with respect to the lithium content. The transition temperature $T_{\mathrm{SP}}$ is suppressed following a square dependence of the lithium concentration while the energy gap is found to decrease linearly. At high temperatures $(T>\mathrm{}{T}_{\mathrm{SP}})$ the susceptibility remains nearly independent of doping.

• Received 2 August 1999

DOI:https://doi.org/10.1103/PhysRevB.61.9523