The Na-TiS2 system: A critical discussion of the phase boundaries,structural and NMR studies

We present new evaluations of phase boundaries in the Na_xTiS₂ system from electrochemical intercalation and from X-ray and NMR measurements in samples intercalated using the liquid ammonia technique. After a critical discussion of the influence of the method of intercalation on the phase limits we present an extensive NMR study of the system. ²³Na quadrupolar coupling determinations support the fact that the low concentration (x < 0.25) phase II is a stage 2 phase. ²³Na Knight shift results show that the transition from the Ib trigonal prismatic phase to the Ia trigonal antiprismatic phase with increasing Na concentration takes place with a change in the electronic band structure. The stability of this phase is discussed in terms of the balance between elastic and electronic energies.