Synchrotron x-ray diffraction and Raman scattering investigations of (LixNa1-x)NbO3 solid solutions:: Evidence of the rhombohedral phase -: art. no. 144105

The (LixNa1-x)NbO3 perovskite solid solutions are investigated using synchrotron x-ray diffraction and Raman spectroscopy in order to clarify the structural changes in the concentration range 0less than or equal toxless than or equal to0.145 at room temperature. The orthorhombic antiferroelectric P phase (space group Pbma, Z=8) exists up to x=0.02 and in the concentration interval 0.02less than or equal toxless than or equal to0.03 we have confirmed a previously reported transition to the orthorhombic ferroelectric Q phase (space group P2(1)ma, Z=4). It is found that the Q phase is stable up to x=0.145 but in the narrow concentration interval at x=0.12 the dominating (86.2%) rhombohedral N phase (space group R3c, Z=2) coexists with the minor (13.8%) Q phase at room temperature. The crystal structure of this rhombohedral N phase has been refined using Rietveld method. Detailed comparison with similar low-temperature phase of pure NaNbO3 showed that the NbO6 octahedra are slightly distorted in the solid solution with x=0.12 while they are rather regular in NaNbO3. Raman spectra showed drastic changes associated with the P-Q transition and revealed coexistence of the P and Q phases in the interval 0.02less than or equal toxless than or equal to0.03. Abrupt transformation of the Raman response and remarkable narrowing of the Nb-O stretching vibrations related to the existence of the rhombohedral N phase at x=0.12 were observed.