lgli (高120cm--宽90cm)(1)

nullnullFig.3. TG-DSC curves of the synthesized 5 at.% Nd-doped SrO(SrTiO3)n (n=1,2) precursor powders (zero gel) dried at 180 °C: (a) n=1; (b) n=2.L.L. Li, R.R. Sun, Y.F.Liu, G.L. Guo and X.Y. Qin Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, 230031 Hefei, P. R. China * Corresponding author: xyqin@issp.ac.cn Synthesis and thermoelectric properties of Nd-doped Ruddlesden-Popper phase SrO(SrTiO3)n (n=1,2) oxides SrTiO3 is a typical transition-metal perovskite-type oxide. In recent years, more focus are given on the thermoelectric properties of SrTiO3 because of the large power factor (PF=S2/ρ,La-doped), 28-36 μW/(K2cm), which is comparable to that of Bi2Te3 at room temperature[1], but the larger thermal conductivity (κ>10 Wm-1K-1) inhibited its practical applications[2]. The natural superlattice structure SrO(SrTiO3)n (n=integer), layered 3d transition-metal oxides and well known as Ruddlesden-Popper (RP) phase[3], has a quasi-two dimensional structure (as shown in Fig.1), which is expected to be a good candidate TE material in high temperature for the possibility to suppress κ by enhanced phonon scattering at the large number of SrO/ SrTiO3 interfaces[4-5].[1] T.Okuda, et al., Phys Rev B 63, 113104 (2001) . [2] S. Ohta, et al., J Appl Phys 97, 034106 (2005) [3] S.N. Ruddlesden, P. Popper, Acta Crystallogr 11 (1958) 54-55. [4] Y.F. Wang, et al., Ceram Int 34 (2008) 849-852. [5] K.H. Lee,et al., J Appl Phys 100，063717 (2006). [6] A. Kikuchi, et al.,Scripta Mater 63 (2010) 407-410 [7] A. Kikuchi, et al., Mater Trans 51 (2010) 1919-1922Fig.1. The crystal structures of Ruddlesden–Popper phase, SrO(SrTiO3)n with (a) n=1 ,(b) n=2 Citation: J. Appl. Phys. 105.103701(2009) The conventional solid-state reaction with hot-press sintering method to prepare the rare-earth metal-doped SrO(SrTiO3)n (n=1,2,∞) is quite time- and energy-consuming. To overcome this problem, spark plasma sintering (SPS), with a higher heating and cooling rate than the hot-press sintering method, can prepare dense ceramic samples in a short time, have been used to synthesize the Sr-Ti-O system thermoelectric materials[6-7]. ReferencesIn the work, we have investigated the combination citrate sol-gel method and SPS to fabricate the dense Nd-doped SrO(SrTiO3)n (n=1,2) ceramics and study the thermoelectric properties. Precursor powder of stoichiometry Nd-doped SrO(SrTiO3)n (n=1,2) were synthesized by a citrate sol-gel method . TG and DSC were used to explore the thermal behavior of the gel. The phase structures and morphologies of precursor powders were studied by XRD and SEM. The single composition in all ceramic samples were prepared by solid-state reaction of the precursor powders under a reducing atmosphere with post-spark plasma sintering for the first time. RP phases precursor powders can be obtained by calcinations of the zero gel powders above 900℃ , but the presence of Nd2O3 phase in the precursor powders signifies that part of the Nd3+ ions may exist in the interstitial of the perovskite structure and Sr2+ can not be substituted completely by Nd3+. After precursor powders were sintered in reducing atmosphere, the single phase was formed in all n=2 compounds, while a small amount of n=2 phase was observed in all n=1 samples as a second phase, indicating that the n=2 phase is more stable than the n=1 phase in the Sr-Ti-O systerm RP phase, as shown in Fig.5 . Fig.6 Temperature dependence of (a) electrical resistivity ρ , (b) Seebeck coefficient S, (c) thermal conductivity κand (d) dimensionless figure of merit ZT for (Sr1-xNdx)n+1TinO3n+1（n=1,2；x=0.05, 0.1） Fig.5. XRD patterns of (Sr1-xNdx)n+1TinO3n+1 （n=1,2；x=0.05, 0.1）samples sintered in reducing atmosphere one time, (a) n=1; （b）n=2.. revealing that all the samples are n-type degenerate semiconductors and the Nd atoms act as electron donors. The estimated electronic thermal conductivity κe values are very small as compared to the total thermal conductivity κ, indicating that lattice contribution is predominant in the RP phase compounds. The ZT values of all Nd-doped samples increase with temperature and the largest ZT value is 0.13 achieved at 905K in10 at.% Nd-doped Sr3Ti2O7. Fig.4 Precursor powders (a) n=1; (b) n=2 ρincreases with increasing temperature, showing a metallic-like behavior, and decreases with the increase of Nd dopant content. All compounds have a negative S, with a gradual increase in magnitude with temperature, The combination of sol-gel synthesis with SPS is suitable for synthesizing thermoelectric oxides. The maximum ZT value (0.13 at 905 K) was observed for 10 at.% Nd-doped Sr3Ti2O7.