Phase transitions near to 300K, in TiH1.99 and TiD1.97, were studied by means of nuclear magnetic resonance techniques. A complex proton line-shape was observed in TiH1.99, at temperatures ranging from 200 to 470K. The proton line-shape in TiH1.99 consisted of the superposition of a weak narrow line and a broad line. It was suggested that the narrow proton line was associated with H that was located in the octahedral sites of the TiH1.99 lattice. A sharp increase in the narrow-line intensity near to 400K indicated a rapid redistribution of H between the tetrahedral and octahedral sites. The broad-line width was 10.5G, both below and above the critical temperature of 295K, and increased to 15.5G near to the critical temperature. The 10.5G line-width was in good agreement with the Van Vleck second moment for protons that were located in the tetrahedral sites of a face-centered cubic TiH2 lattice. The proton line-width in TiH1.99 did not depend upon the applied magnetic field strength, so a substantial broadening of the line-width was attributed to an increase in magnetic dipole-dipole interactions. Therefore, a substantial broadening of the proton line-width near to the critical temperature was attributed to a cooperative Jahn-Teller mechanism in TiH2. This purported cooperative Jahn-Teller phase transition was supported by an investigation of this phase transition in TiD1.97, where a quadrupolar broadening of the 2D nuclear magnetic resonance line was observed above its critical temperature of 310K. The difference of about 15K between the critical temperatures of TiH1.99 and TiD1.97 was an isotopic effect, as confirmed by heat capacity measurements.

Z.I.Kudabaev, D.R.Torgeson, A.F.Shevakin: Journal of Alloys and Compounds, 1995, 231, 233-7