k
7
Li, 31P and 1H Static and MAS NMR investigations in the
mixed crystals Li(1-x)(NH4)xH2PO4 (0.3 ≤ x ≤ 0.7)
R. P. Sreekanth Chakradhar* K.P. Ramesh and J. Ramakrishna
Department of Physics, Indian Institute of Science, Bangalore - 560 012, India.
Abstract
Mixed crystals Li(1-x)(NH4)xH2PO4 (0.3 ≤ x ≤ 0.7) were grown over a wide range of
composition from an aqueous solution and are studied by X-ray diffraction and NMR.
The
7
Li,
31
P and 1H static and MAS NMR exhibit a marked composition dependence.
Room temperature 7Li NMR spectra shows an increased motional narrowing with an
increase of Li content indicating an overall increase in mobility of Li ions. The MAS
spectrum exhibits a sharp peak with the resolution width which is consistent with the
average of static dipolar interactions. All these observations clearly indicate that, at room
temperature the transverse relaxation and the second order quodrupole interactions are
negligible contributions in comparison with the static dipolar interaction. At high
temperatures the central linewidth was drastically reduced corresponding to the averaging
of zero dipolar interactions by motional narrowing. The results obtained on 7Li, 31P and
1
H have been discussed in detail as a function of x as well as temperature.
*Corresponding Author e-mail : chakra72@physics.iisc.ernet.in