Raman investigation and functional characterization of (Pb0.8La0.2)(Mg0.4Nb0.6)O3 ceramics prepared by the columbite method

(Pb0.8La0.2)(Mg0.4Nb0.6)O3 relaxor ceramics have been prepared by columbite method by using (i) MgO and (ii) (MgCO3)4·Mg(OH)2·4H2O precursors (denoted as PLMN1 and PLMN2 respectively). The dielectric data show relaxor behaviour in the frequency range of 10 Hz to 1 MHz, with dielectric constant values in the range of 310–350 for PLMN1 and 240–260 for PLMN2 and a permittivity maxima at the temperature Tm = 179 K and Tm = 174 K, respectively (for f = 1 MHz). The Raman spectra proved the stability of the nanopolar order far above Tm, as observed in many Pb-based relaxors. This is demonstrated by the existence of some modes (at ∼300, 500 and 780 cm−1) up to around 773 K. Anomalies of some Raman modes (integrated intensity and FWHM) have been found in the range of Tm, proving the phase transition from pseudo-cubic relaxor to cubic paraelectric state, where the stability of the vibration modes is affected by the fluctuations associated to the phase transitions.

Research highlights▶ Pb0.8La0.2)(Mg0.4Nb0.6)O3 ceramics were prepared by columbite method starting with two Mg precursors. ▶ The Mg precursor influenced the densification and the functional properties of PLMN ceramics. ▶ The Mg precursor seems to have not a significant influence on the value of the temperature of the permittivity maximum. ▶ The Raman spectra were analyzed and proved the stability of the nanopolar order far above Tm.