DSpace at VNU: La Sm Er Cation Doping Induced Thermal Properties of SrTiO3 Perovskite

Article pubs.acs.org/IC La/Sm/Er Cation Doping Induced Thermal Properties of SrTiO3 Perovskite Meena Rittiruam,†,‡ Tosawat Seetawan,*,†,‡ Sirakan Yokhasing,†,‡ Korakot Matarat,‡,§ Phan Bach Thang,∥,⊥ Manish Kumar,# and Jeon Geon Han# † Program of Physics, Faculty of Science and Technology, Sakon Nakhon Rajabhat University, 680 Nittayo, Mueang District, Sakon Nakhon, 74000, Thailand ‡ Simulation Research Laboratory, Center of Excellence on Alternative Energy, Research Development Institute, Sakon Nakhon Rajabhat University, 680 Nittayo, Mueang District, Sakon Nakhon, 74000, Thailand § Program of Computer, Faculty of Science and Technology, Sakon Nakhon Rajabhat University, 680 Nittayo, Mueang District, Sakon Nakhon, 74000, Thailand ∥ Faculty of Materials Science, University of Science, Vietnam National University, 227 Nguyen Van Cu, Ward 4, District 5, Ho Chi Minh City, Vietnam ⊥ Laboratory of Advanced Materials, University of Science, Vietnam National University, 227 Nguyen Van Cu, Ward 4, District 5, Ho Chi Minh City, Vietnam # Center for Advanced Plasma Surface Technology, NU-SKKU Joint Institute for Plasma Nano-Materials, Advanced Materials Science and Engineering Sungkyunkwan University, Suwon 440746, Korea ABSTRACT: The La/Sm/Er cations with different radii doping SrTiO3 (STO) as model Sr0.9R0.1TiO3 (R = La, Sm, Er) were designed to investigate structural characteristics and thermal properties by the molecular dynamics simulation with the Green−Kubo relation at 300−2000 K The structural characteristics were composed of lattice constant, atoms excursion, and pair correlation function (PCF) The thermal properties consisted of heat capacity and thermal conductivity The lattice constant of R-doped exhibited less than the STO at 300−1100 K and more than STO at 1500−2000 K, which was encouraged by atom excursion and PCF The thermal properties was compared with literature data at 300−1100 K In addition, the thermal properties at 1100−2000 K were predicted It highlights that thermal conductivity tends to decrease at high temperature, due to perturbation of La, Sm, and Er, respectively important for another application such as fuel cells,8 gas sensors,9 and STO substrate of YBCO superconductors.10,11 We propose calculating the newly thermal properties of Rdoped STO composed of lattice constant, atomic exclusion, PCF, heat capacity, thermal conductivity with time correlation, and thermal conductivity at various temperatures Thermal properties of R-doped STO, which propose to reduce thermal conductivity We selected the rare earth of La is similarly radius, Sm is large radius and Er is small radius to investigate and describe on thermal properties of R-doping STO at high temperature In addition, the doping of lanthanum causes small changes in thermal conductivity.12−14 The formation of the Ruddlesden−Popper phase does lead to the desired decrease in thermal conductivity, but also leads to a decrease in electrical conductivity, which limits the impact on the figure of merit.15 INTRODUCTION Thermoelectricity involves the conversion of thermal energy directly into electrical energy; the development of thermoelectric (TE) materials has become very important and much needed The performance of TE materials can be evaluated by a dimensionless figure of merit in the equation: ZT = S2σT/κ Ideally, good TE materials exhibit a large Seebeck coefficient (S), high electrical conductivity (σ), and low thermal conductivity (κ) when both such conductivities are measured at absolute temperature (T).1 STO is a material of considerable interest and an n-type and strong candidate of oxide TE materials.1−4 Recently, the rare earth (R) doping in STO enhancing TE properties was reported.2,5,6 The R-doped STO shows high κ,5; the κ has been important to TE properties as well as the thermal properties, composed of lattice constant versus temperature, atomic exclusion, PCF, and heat capacity, which have been important to reduce thermal conductivity too.7 However, the thermal properties of R-doped STO are not reported by the literature data.2,5,6 In addition, the thermal properties have been © XXXX American Chemical Society Received: June 7, 2016 A DOI: 10.1021/acs.inorgchem.6b01313 Inorg Chem XXXX, XXX, XXX−XXX Article Inorganic Chemistry COMPUTATIONAL DETAILS RESULTS AND DISCUSSION Structural Characteristics The Sr La TiO , Sr0.9Sm0.1TiO3, and Sr0.9Er0.1TiO3 were obtained as cubic structures and show the lattice constant values of a = b = c = 3.8959 ± 0.0023 Å, 3.8996 ± 0.0022 Å, and 3.8990 ± 0.0021 Å at room temperature, respectively Figure shows the lattice 16 The molecular dynamics method with Verlet’s algorithm and Ewald’s summation17 based on MXDORTO18 provide a means of the structural and thermal properties The cluster atoms model of Sr0.9R0.1TiO3 was designed by the crystal data of the STO perovskite structure19 with 320 atoms (O = 192, Ti = 64, Sr = 58, R = 6) based on MXDTRICL,18 as shown in Figure Figure Cluster atoms model for Sr58R6Ti64O192 (R = La, Sm, Er) designed by MXDTRICL The atomics interaction was determined by combination of the Morse-type20 with the Busing−Ida potential function,21 as shown in eq 1.22 The potential parameters of the cluster atoms model are present in Table zizje Uij(rij) = rij Figure Calculated lattice constant for Sr0.9R0.1TiO3 (R = La, Sm, Er) at various temperatures ⎛ + aj − rij ⎞ cicj ⎟⎟ − + f0 (bi + bj)exp⎜⎜ rij6 ⎝ bi + bj ⎠ constant of La-, Sm-, and Er-doped STO with calculation and experimental data The potential parameter is the cause of the lattice constant agreeing with experimental data.5,26,27 The lattice constant versus temperature was compared with MD calculation of STO as in a previous work.7 It was found that the calculated lattice constants after substitution to compare with STO show decreased at 300−1100 K and increased at 1500− 2000 K The structural expansion was described by atoms excursion as shown in Figure These calculations suggest that the Sr-site shows large atomic excursion, while the O-site and Ti-site show small atomic exclusion (Figure 3), which contribute to the increase or decrease of the lattice constants by the Sr-site (Asite) These findings help to understand the lattice constant increase at high temperature, while the error value has been also increased The atomic excursion in the unit cell has small vibration at low temperature and large vibration at high temperature together with high error value The PCF of La-, Sm-, and Er-doped STO was highlighted as shown in Figure The shape peak PCF of Ti−O, O−O, and Sr−Ti were indicated explicitly a crystal The neighbor atomic distance of Sr−O, La−O, Sm−O, and Er−O show a values about 2−3 Å The atomic distance of La−Ti, Sm−Ti, and Er−Ti show a value about 1.5−2.5 Å La, Sm and Er affect to decrease total peak of bonding Sr−O also indicated that these substitute affect to decrease crystallography The bonding of Er−O was clearly increase distance from about 1.5 Å In addition, we have rewrite a label of data in Figure 4c Thermal Properties The heat capacity was determined by the lattice constant and internal energy as eqs and + Dij{exp[− 2βij(rij − rij*)] − exp[− βij(rij − rij*)]} (1) Table Interatomic Potential Parameters of Sr58R6Ti64O192 (R = La, Sm, and Er) atom z a (Å) b (Å) c (kJ1/2 Å3 mol−1/2) −1.2 O Ti Sr La, Sm, Er atom pair Ti−O Sr−O La−O Sm−O Er−O 1.9232 (La) 1.926 (Sm) 1.9256 (Er) 1.2 1.055 1.2 1.198 1.2 0.6 D (10−19 J) 0.16 20 0.18 0.16 0.16 β (Å−1) 25 10 r* (Å) 4.3 2.41 2.60 2.60 2.60 3.82 1.18 1.18 1.18 1.18 2.1923 2.7615 2.7615 2.7615 2.7615 where f is the repulsion between atoms in vacuum equal to 4.186, zi is the effective partial electronic charges on the ith ions, zj is the effective partial electronic charges on the jth ions, rij is the interatomic distance, rij* is the bond length of the cation−anion pair in vacuum a, b, and c describe the characteristic parameters which are dependent on the ion species Dij and βij describe the depth and shape of this potential, respectively The temperature and pressure were controlled by Nose,23 and Andersen method,24 respectively as same previous work25 for calculation of lattice constant, heat capacity, and thermal conductivity To confirm the accuracy, the lattice constant, heat capacity, and thermal conductivity were calculated 106 steps for equilibrium state of system CP = CV + Cd B (2) DOI: 10.1021/acs.inorgchem.6b01313 Inorg Chem XXXX, XXX, XXX−XXX Article Inorganic Chemistry Figure Calculation of atoms excursion in unit cell of Sr0.9R0.1TiO3 (R = La, Sm, Er) at temperature 300 K Figure Pair correlation function (PCF) of (a) O−O, Ti−O, and Ti−Ti; (b) Sr−Ti, La−Ti, Sm−Ti, and Er−Ti; (c) Sr−Sr, La−Sr, Sm−Sr, and Er−Sr; and (d) Sr−O, La−O, Sm−O, and Er−O various distances at temperature 300 K Figure Heat capacity for Sr0.9R0.1TiO3 (R = La, Sm, Er) at various temperatures is calculated C DOI: 10.1021/acs.inorgchem.6b01313 Inorg Chem XXXX, XXX, XXX−XXX Article Inorganic Chemistry Figure Thermal conductivity for Sr0.9R0.1TiO3 (R = La, Sm, Er) is calculated at 300 K ⎛ ∂E(T ) ⎞ (3αlin)2 Vm(T ) ⎟ + CP = ⎜ T ⎝ ∂T ⎠V β κlat = −1⎛ ⎛ ∂E(T ) ⎞ 3a(P0)Vm(T )T ⎛ ∂a(P) ⎞ a(T ) − a(T0) ⎞ ⎟ + ⎜ ⎟ ⎜ =⎜ ⎟ ⎝ ∂T ⎠V ⎝ ∂P ⎠T ⎝ T − T0 ⎠ a(T0)2 P V 3kBT τ =∞ ∫τ=0 S(t )d τ V (4) where V is volume of the unit cell, kB is Boltzmann constant, S(t) is heat flux autocorrelation function, and τ is time correlation The thermal conductivity was evaluated from the heat flux autocorrelation function which the function calculated 10 times, as shown in Figure The thermal conductivity of Ladoped STO shows a value of 5.9 W m−1 K−1 at a time correlation of 1.4 ps The thermal conductivities of Sm- and Erdoped STO show 5.49 and 4.1 W m−1 K−1 at a time correlation of ps, respectively The calculated thermal conductivity for Sr0.9R0.1TiO3 (R = La, Sm, Er) at various temperatures together with literature data is shown in Figure The results present thermal conductivity at 300−2000 K, while literature data were also reported at 300−1200 K We compare the results of all samples with previous work, which shows that values are less than (3) where CP, CV, and Cd are heat capacity at constant pressure, constant volume, and heat capacity of lattice dilatational term, respectively E(T) is total internal energy, αlin is linear thermal expansion coefficient, β is compressibility, Vm is molar volume, a(P) is lattice parameter at pressure P (Pa), P0 is atmosphere pressure (1 MPa), a(T) is lattice parameter at temperature T (K), and T0 is room temperature The heat capacities of R-doped STO and STO together with the literature7,27 were highlighted as shown in Figure The Cd of R-doped STO was exhibited larger than literature data of STO at the temperature range of 300−1800 K.7 The atoms of La, Sm, and Er obtained larger excursion than Sr (Figure 3) In addition, the Vm of Sm-doped STO shows 35.75 cm3 mol−1, and La- and Er-doped STO show 35.6 and 35.7 cm3 mol−1 at 300 K, respectively, in which they are similar at low temperature and different at high temperature See that the heat capacity of R-doped STO was independent of the temperature range 1300−2000 K The heat capacity has been more fluctuation at 1100−2000 K indicate more error data The total thermal conductivity (κtotal) could be determined by the sum of other terms including lattice thermal conductivity (κlat),28 electron thermal conductivity (κe),29 and bipolar electronic thermal conductivity (κb).30 The oxide TE material exhibits κe and other terms are dependent on electrical transport which exhibit low electrical conductivity; thus, the main term of thermal conductivity can be assumed as κtotal ≈ κlat The κlat was obtained by using the Green−Kubo relation as eq 425 Figure Thermal conductivity for Sr0.9R0.1TiO3 (R = La, Sm, Er) at various temperatures is calculated D DOI: 10.1021/acs.inorgchem.6b01313 Inorg Chem XXXX, XXX, XXX−XXX Article Inorganic Chemistry STO.31 It should be noted that La, Sm, and Er disturb a structure STO at the A-site, which is supported by PCF and time correlation of thermal conductivity (Figure 6) The thermal conductivity of La-doped STO value is 5.99 W m−1 K−1 at room temperature, which agrees with literature data.5,32,33 The thermal conductivity of Sm- and Er-doped STO values are 5.49 and 1.14 W m−1 K−1 at room temperature, respectively, which agree with literature data.5 The La-doped STO exhibits correspond with literature at 520 K,5,32,33 and good agreement with data of Liu5 at 580−1100 K On the other hand, the Sm-, and Er-doped STO exhibits lower than data of Liu5 at least 400 K The doped sample shows a significant value of 1.75 W m−1 K−1 for La-doped, 1.30 W m−1 K−1 for Sm-doped, and 1.10 W m−1 K−1 for Er-doped at 2000 K, respectively (11) Hayward, S A.; Salje, E K H Phase Transitions 1999, 68, 501− 522 (12) Ohta, S.; Nomura, T.; Ohta, H.; Koumoto, K J Appl Phys 2005, 97, 034106 (13) Liu, J.; Wang, C L.; Su, W B.; Wang, H C.; Zheng, P.; Li, J C Appl Phys 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Er have larger excursion than Sr It contributed to the increase of heat capacity The thermal conductivity has been reduced with literature data at the temperature range of 300−1100 K Moreover, we predicted the thermal conductivity of Sr0.9R0.1TiO3 (R = La, Sm, Er) at a temperature of 1100− 2000 K, which decreases to about W m−1 K−1 ■ AUTHOR INFORMATION Corresponding Author *E-mail: t_seetawan@snru.ac.th Notes The authors declare no competing financial interest ■ ACKNOWLEDGMENTS This work was supported by Thailand Research Fund (TRF) through the Royal Golden Jubilee (RGJ) Ph.D Program (Grant No PHD/0195/2558) ■ REFERENCES (1) Rowe, D M., Ed Thermoelectrics Handbook: Macro to Nano; Taylor & Francis: New York, 2006 (2) Muta, H.; Kurosaki, K.; Yamanaka, S J Alloys Compd 2003, 350, 292−295 (3) Muta, H.; Kurosaki, K.; Yamanaka, S J Alloys Compd 2004, 368, 22−24 (4) Fukuyado, J.; Narikiyo, K.; Akaki, M.; Kuwahara, H.; Okuda, T Phys Rev B: Condens Matter Mater Phys 2012, 85, 075112 (5) Liu, 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sum of other terms including lattice thermal conductivity (κlat),28 electron thermal. .. molar volume, a(P) is lattice parameter at pressure P (Pa), P0 is atmosphere pressure (1 MPa), a(T) is lattice parameter at temperature T (K), and T0 is room temperature The heat capacities of