Synthesis, structure and electrical properties of Li 1+ x + y Sc x Y y Ti 2 - x - y (PO 4 ) 3 (x = 0.15–0.3, y = 0.01–0.15) ceramics A.F. Orliukas a, ⁎ , T. Šalkus a , A. Dindune b , Z. Kanepe b , J. Ronis b , A. Určinskas a , E. Kazakevičius a , A. Kežionis a , V. Kazlauskienė c , J. Miškinis c a Faculty of Physics, Vilnius University, Saulėtekio al. 9/3, LT-10222 Vilnius, Lithuania b Institute of Inorganic Chemistry, Riga Technical University, Miera 34, LV-2169 Salaspils, Latvia c Institute of Materials Science and Applied Research, Vilnius University, Sauletekio al. 9/3, LT-10222 Vilnius, Lithuania Abstract The powder of Li 1+ x + y Sc x Y y Ti 2 - x - y (PO 4 ) 3 (x = 0.15–0.3, y = 0.01–0.15) has been synthesized by solid phase reaction. The structure of the compounds was determined by X-ray diffraction patterns from the powder. The compounds belong to the rhombohedral symmetry (space group R3¯c) with Z = 6 formula units in the lattice. Ceramic samples were sintered in air at temperature T s = 1523 K varying sintering time (t s ) from 1 to 5 h. The element compositions of ceramics were defined by XPS. The complex impedance (Z ˜ ), electric conductivity (σ ˜ ), dielectric permittivity (ɛ ˜ ) of the ceramics in frequency range (10 6 -1.2 · 10 9 ) Hz and temperature range (300-600) K were carried out. Two relaxation dispersions of the electric parameters were found for all compounds. The dispersions are caused by the ion transport in grains and grain boundaries of the ceramic samples. The values of the bulk (σ b ), grain boundaries (σ gb ) conductivities, their activation energies, and dielectric permittivity are dependent on stoichiometric parameters x, y and sintering conditions of the ceramics. © 2007 Elsevier B.V. All rights reserved. Keywords: Ionic conductivity; Solid electrolyte ceramics; Permittivity; Synthesis; Sintering 1. Introduction The partial substitution of Ti 4+ by trivalent ions M = Al 3+ , Sc 3+ , Fe 3+ , Ga 3+ , In 3+ , Cr 3+ ,Y 3+ in the NASICON-type net- work structure of LiTi 2 (PO 4 ) 3 compound causes the increase of the value of the Li-ion conductivity of Li 1+ x M x Ti 2 - x (PO 4 ) 3 systems [1–5]. The Li + ion transport number in these com- pounds was found to be 100% [6]. The influence of substitution Ti 4+ by Sc 3+ in LiTi 2 (PO 4 ) 3 on structure and electric properties was discussed in [1–3]. At room temperature LiTi 2 (PO 4 ) 3 and Li 1+ x Sc x Ti 2 - x (PO 4 ) 3 (where x =0–0.3) compounds belong to rhombohedral symmetry with the space group R3 ¯c [1]. The lattice parameters a = 8.504 Å, c =20.840 Å for LiTi 2 (PO 4 ) 3 and a = 8.559 Å, c =20.964 Å for Li 1.3 Sc 0.3 Ti 1.7 (PO 4 ) 3 and depend on stoichiometric factor x [3]. The highest total ionic conductivity was found for Li 1.3 Sc 0.3 Ti 1.7 (PO 4 ) 3 compound (at room tempera- ture σ t = 4.07 · 10 - 2 S/m and its activation energy ΔE t = 0.4 eV) [3]. The replacement of the Ti 4+ by Y 3+ in LiTi 2 (PO 4 ) 3 resulted mixed phases LiTi 2 (PO 4 ) 3 and Li 3 Y 2 (PO 4 ) 3 [1]. The authors [2,5,6] synthesized Li 1+ x Y x Ti 2 - x (PO 4 ) 3 (x = 0.3, 0.4) compounds by solid phase reaction and reported that so synthesized compounds are single phase materials and belong to rhombohe- dral symmetry (space group R3 ¯c). The lattice parameters of Li 1.4 Y 0.4 Ti 1.6 (PO 4 ) 3 are a =8.5086(5) Å, c =20.8261(31) Å and cell volume V = 1305.75 Å 3 [5]. The value of total conductivity at room temperature of the Li 1.4 Y 0.4 Ti 1.6 (PO 4 ) 3 ceramics was found to be σ t =4.5·10 - 3 S·m - 1 and its activation energy ΔE t = 0.3 eV [5]. The values of σ t are dependent on sintering time (t s ) of ceramic samples [5]. The Li + ion transport number in the compound is 100% [6]. Today, Li + ion conductors are used for variety of technical applications, namely as solid electrolytes in high energy batteries [7] and sensitive CO 2 gas sensors [8]. In the present work we are going to investigate the conditions for the synthesis of Li 1+ x + y Sc x Y y Ti 2 - x - y (PO 4 ) 3 (x = 0.15–0.3, y = 0.01–0.15) powder, sintering of the ceramic samples, deter- mine crystal structure, elemental compositions and measure the electric properties of the ceramics in the frequency range Available online at www.sciencedirect.com Solid State Ionics 179 (2008) 159 – 163 www.elsevier.com/locate/ssi ⁎ Corresponding author. E-mail address: antanas.orliukas@ff.vu.lt (A.F. Orliukas). 0167-2738/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2007.12.036