High temperature phase stability in Li0.12Na0.88NbO3: A combined powder X-ray and neutron diffraction study

Abstract

The phase stabilities of ecofriendly piezoelectric material of lithium doped sodium niobate for composition Li0.12Na0.88NbO3 (LNN12) have been investigated by a combination of powder X-ray and neutron diffraction techniques in the temperature range of 300-1100K. We observed interesting changes with appearance or disappearance of the super-lattice reflections in the powder diffraction patterns. Unambiguous experimental evidence is shown for coexistence of paraelectric and ferroelectric orthorhombic phases in the temperature range of 525K to 675K. We identified the correct crystal structure of LNN12 with temperature and correlated it with observed anomaly in the physical properties. Identification of crystal structure also helps in the mode assignments in Raman and infrared spectroscopies. We argued that application of chemical pressure as a result of Li substitution in NaNbO3 matrix favors the freezing of zone centre phonons in contrast to the freezing of zone boundary phonons in pure NaNbO3 with the variation of temperature.