Na1−xLixNbO3 ceramics studied by X-ray diffraction, dielectric, pyroelectric, piezoelectric and Raman spectroscopy

Na1−xLixNbO3 ceramics with composition 0.05≤x≤0.30 were prepared by solid-state reaction method and sintered in the temperature range 1100–1150 °C. These ceramics were characterised by X-ray diffraction as well as dielectric permittivity measurements and Raman spectroscopy. Dielectric properties of ceramics belonging to the whole composition domain were investigated in a broad range of temperatures from 300 to 750 K and frequencies from 0.1 to 200 kHz. The Rietveld refinement powder X-ray diffraction analysis showed that these ceramics have a single phase of perovskite structure with orthorhombic symmetry for x≤0.15 and two phases coexistence of rhombohedral and orthorhombic above x=0.20. The evolution of the permittivity as a function of temperature and frequency showed that these ceramics Na1−xLixNbO3 with composition 0.05≤x≤0.15 present the classical ferroelectric character and the phase transition temperature TC increases as x content increases. The polarisation state was checked by pyroelectric and piezoelectric measurements. For x=0.05, the piezoelectric coefficient d31 is of 2pC/N. The evolution of the Raman spectra was studied as a function of temperatures and compositions. The results of the Raman spectroscopy study confirm our dielectric measurements, and they indicate clearly the transition from the polar ferroelectric phase to the non-polar paraelectric one.

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► XRD shows that NLN ceramics is a single phase of orthorhombic structure for x≤0.15.
► Two phases coexistence of rhombohedral and orthorhombic above x=0.20.
► Dielectric measurements show that for 0.05≤x≤0.15: NLN is a classical ferroelectric.
► Polarisation state was checked by pyroelectric and piezoelectric measurements.
► Raman spectra evolution was studied as a function of temperatures and compositions.