Incorporation of lanthanide ions in lead titanate

Abstract

A series of lanthanide, Ln, ion doped lead titanate ceramics, at 2 and 8 at.%, have been prepared with starting compositions Pb 1-3x/2 Ln x TiO 3 , Ln = La, Nd, Sm, Eu, Gd, Dy, using a standard ceramic method. Structural, and differential scanning calorimetry, measurements are reported. Doping with La 3+ results in a reduction in tetragonality and cell volume; a partial recovery was then observed for the smaller Ln 3+ ions and suggests the onset of partial substitution of the rare earth on the B-site. The ferroelectricparaelectric transition temperature results also consistent with an increased probability the B-site occupation with decreasing ion size.

Study ofAandBsites order in lanthanide-doped lead titanate ferroelectric system

“…It is well known that there is a direct correspondence of the soft mode with the tetragonal distortion [( c / a ) − 1 relation] (Dobal and Katiyar, 2002). Previous XRD experiments have shown an increase of the [( c / a ) − 1] values with the decrease of the ionic radii of the rare earths (Peláiz-Barranco et al , 2012). It could be expected an increase of [ E (1TO)] 2 as well (Figure 2).…”

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Figure 2. Squared frequency of the E (1TO) soft mode as function of [( c / a ) − 1]. The data for the undoped lead titanate were taken from the previous papers (Paris et al , 2008; Peláiz-Barranco et al , 2012).

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“…The structure data were taken from the “Inorganic Crystal Structure Database” (ICSD) (FIZ Karlsruhe, 2014). In the initial structural model, the experimental evidence from the Raman spectra and the results of the previous structural studies suggesting the incorporation of the lanthanide ions at both A and B sites have been considered (Mackie et al , 2010; Mendez-González et al , 2010, 2014; Peláiz-Barranco et al , 2010, 2012). The general nominal composition was Pb 0.94 Ln 0.04 Ti 0.96 Ln 0.04 O 2.98 taking into account that the initial occupancy of Ln 3+ at B site should be in correspondence with the calculated tolerance factor value for these compositions (Mendez-González et al , 2010, 2014; Peláiz-Barranco et al , 2012).…”

“…The incorporation of rare-earth ions into A and/or B sites is an issue of interest in perovskite oxides titanates (García-Zaldívar et al , 1997; Buscaglia et al , 2000, 2002, 2004; Peláiz-Barranco et al , 2009, 2010, 2012; Mackie et al , 2010; Mendez-González et al , 2010, 2014). Previous studies, in BT ceramics, have shown that Ba 2+ can be substituted by La 3+ and Pr 3+ ions, while fractional occupancy of Gd 3+ and Tb 3+ at the B site has been predicted (Buscaglia et al , 2000).…”

“…Recently, a structural study using the extended X-ray absorption fine structure technique and Rietveld refinement on a PT compound modified with 8 at% of Eu 3+ has shown the incorporation of this ion at both sites of the perovskite structure (Mendez-González et al , 2014). Indirect evidence on the possible incorporation of lanthanide elements at both crystallographic sites has been established from positron annihilation lifetime spectroscopy measurements on rare-earth-doped PT ceramics (Peláiz-Barranco et al , 2012). The results have shown, qualitatively, a higher occupancy at the A site for La 3+, Nd 3+ , and Eu 3+ ions, while smaller ions (Gd 3+ and Dy 3+ ) mostly prefer to occupy the B site.…”