Anomalous structural feature of ${\mathrm{LiNbO}}_3$ observed using neutron diffraction

An anomalous structural effect has been observed and analyzed on ${\mathrm{LiNbO}}_3$ at low temperature by neutron-diffraction experiments. Two minima in the unit-cell volume at 55 and 100 K related with maxima and minima in the volume vibrational isotropic factors of Li and Nb atoms, respectively, and a change in the curve slope of the spontaneous stress at 55 K have been identified. This fact, together with the shortening in distance of the Li and O layers at 55 K, has been related with variations in the Ps factor through the secondary pyroelectric effect.

Figure 1

Variation of the ${\mathrm{LiNbO}}_3$ cell volume versus temperature on the D1B neutron beamline.

Figure 2

Variation of the ${\mathrm{LiNbO}}_3$ cell volume versus temperature calculated after Rietveld refinement of the neutron-diffraction patterns from the D1A neutron beamline (a); (b) shows a zoom of (a) where variation of volume of the unit cell with temperature in the range 10–110 K is displayed.

Figure 3

(a) ${\mathrm{LiNbO}}_3$ neutron-diffraction pattern obtained with the D1B beamline. (b) ${\mathrm{LiNbO}}_3$ neutron-diffraction pattern obtained with the D1A beamline.

Figure 4

Dependence of the isotropic thermal parameter for Li (a) and Nb (b) atoms with temperature (in the range 10–200 K).

Figure 5

Variation of the $Z$ atomic coordinates for Li (a) and O (b) atoms with temperature in the range 10–200 K.

Figure 6

Spontaneous strain versus temperature.