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On ion transport mechanism in K+-conducting solid electrolytes based on K3PO4
Solid State Ionics 265 (2014) 46–48
Contents lists available at ScienceDirect
Solid State Ionics journal homepage: www.elsevier.com/locate/ssi
On ion transport mechanism in K+-conducting solid electrolytes based on K3PO4 E.I. Burmakin, G.Sh. Shekhtman ⁎ Institute of High Temperature Electrochemistry Urals Branch RAS, S.Kovalevskoy Street 22, 620990 Ekaterinburg, Russian Federation
a r t i c l e
i n f o
Article history: Received 14 March 2014 Received in revised form 27 June 2014 Accepted 16 July 2014 Available online xxxx Keywords: Solid electrolytes Potassium ion conductivity Potassium orthophosphate
a b s t r a c t Data on transport properties of potassium conducting solid electrolytes based on K3PO 4 in the systems K3 − 2xMxPO4 (M = Mg, Ca, Sr, Ba, Zn, Cd, Pb) and K3 − xP 1 − xE xO4 (E = S, Cr, Mo, W) have been analyzed. The results indicate that, in addition to the usual hopping mechanism, a substantial significance for ion transport in similar phases belongs to the “paddle wheel” mechanism. This mechanism is due to orientation disorder of the PO4 tetrahedra at elevated temperatures, which promotes moving K+ ions to the neighboring vacant positions. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Potassium orthophosphate K3PO4 has a rather high potassium ion conductivity at elevated temperatures, which is 5 × 10−4–5 × 10−2 S cm−1 in 400–800 °C temperature range [1]. Heterovalent substitutions which lead to potassium vacancy creation, such as 2 K+ → M2+ + VK or P5+ + K+ → E6+ + VK, are accompanied by the formation of solid solutions [2–5] whose K+-ion conductivity reaches 10−2 S cm−1 at 300 °C [5–8]. These values are among the best ones for polycrystalline potassium conducting solid electrolytes [9–11]. While analyzing the results obtained for K3 − 2xMxPO4 (M = Mg, Ca, Sr, Ba, Zn, Cd, Pb), we considered the influence of ionic radius of M2+ and the effect of complex formation at high level of doping on potassium ion transport [6,12,13]. These factors are certainly of importance for hopping ionic transport, but the analysis of experimental data as a whole shows that there exists an additional factor that influences ionic transport in such systems. 2. Results and discussion At room temperature K3PO4 is orthorhombic, space group Pnma, a = 1.12377(2), b = 0.81046(1), c = 0.59227(1) nm, z = 4 [14]. With increasing temperature, low temperature orthorhombic γ-form of K3PO4 transforms into a high temperature fcc β one, space group Fm3, a = 0.811 nm, z = 4 [15,16]. The temperature of γ ↔ β transition is 550 ± 10 °C [1,2,16]. The cubic β polymorph of potassium orthophosphate forms extensive ranges of solid solutions when 2 K → M2+ + VK or K+ + P5+ → E6+ + VK replacing mechanism is applied, and the cubic lattice in most such cases is stable down to room temperature. In this ⁎ Corresponding author. E-mail address: [email protected] (G.S. Shekhtman).
http://dx.doi.org/10.1016/j.ssi.2014.07.011 0167-2738/© 2014 Elsevier B.V. All rights reserved.
work we compared the data obtained for K3 − 2xMxPO4 (M = Mg, Ca, Sr, Ba, Zn, Cd, Pb) and K3 − xP1 − xExO4 (E = S, Cr, Mo, W) systems for samples with the same “x” value and crystal lattice (fcc β — form of K3PO4). The value of “x” in every range of systems corresponds to the samples whose composition lies within single-phase β-K3PO4 region, not too close to its boundary. For the first range of systems these requirements were met by samples with x = 0.15, for the second one — 0.10. All the values of activation energy are cited for high temperature flat region of lgσ − 1 / T dependences (400–750 °C). In the low temperature region deviations from linearity were observed in some cases, which made it difficult to define the activation energy adequately. Fig. 1 shows conductivity activation energy against M2+ ionic radius. As one can see, there is no correlation between E and r(M2+). Proceeding from this, we decided to analyze the influence of the crystal structure peculiarities of β-K3PO4 on ion transport of the solid solutions under discussion. It is well known that for a number of phases based on isolated ZO4 tetrahedra there exists orientation disordering of these tetrahedra at elevated temperatures. The best known example is Li2SO4 which was examined in detail by Lunden [17–19]. It was shown that the reorientation of SO4 tetrahedra enhances the mobility of Li+ ions and ionic conductivity by the so called “paddle-wheel” mechanism. According to “paddle-wheel” mechanism contributions to enhanced Li+ ions mobility are expected to come from two sources. One is from the rotatory motion of SO4 tetrahedra which pushes the lithium ions. The other is from the lowering of potential barrier making it easier for a vibrating Li+ ion to jump to an empty adjacent position. In such a case the usual “hopping” conductivity mechanism remains in force too, so the “paddle-wheel” is not the only mechanism but an additional one which quickens the total ionic transport and decreases effective activation energy. A similar mechanism was later proposed for the interpretation of ionic conductivity in alkali nitrates and perchlorates
E.I. Burmakin, G.S. Shekhtman / Solid State Ionics 265 (2014) 46–48
47
Fig. 1. Dependence of the ac conductivity activation energy for K2.70M0.15PO4 solid electrolytes on M2+ ionic radius. Values of ionic radii are taken from ref. [37].
Fig. 3. Dependence of the ac conductivity activation energy for K2.90P0.90E0.10O4 solid electrolytes on E6+ ionic radius. Values of ionic radii are taken from ref. [37].
[20–22]. After that we showed by high temperature neutron diffraction that the high-temperature form of Cs3PO4 may be also considered orientation-disordered or rotor phase [23,24]. As Cs3PO4 and K3PO4 are similar in structure, it can be assumed that the transport of K+ ions in β-K3PO4 based solid solutions is strongly correlated to the rotation of the PO4 tetrahedra. According to the literature data, diffusion coefficients of mono- and divalent cations in Li2SO4 are of the same order of magnitude [25]. Therefore, in orientation-disordered phases both mono- and double-charged cations are mobile [26,27], which means that in the case of K3 − 2xMxPO4 the reorientational rotatory motion of PO4 tetrahedra will push both K+ and M2+ ions to the empty adjacent positions. The rate of rotation of PO4 tetrahedra in such a case will depend on M2+ ionic mass: the higher the M2+ ionic mass, the bigger the energy barrier for M2 + pushing. As Fig. 2 shows, experimental data and the proposed model are in good agreement: there is a strong correlation between conductivity activation energy and relative atomic mass of M. The results of studying K3 − xP1 − xExO4 (E = S, Cr, Mo, W) systems [5] confirm the influence of PO4 tetrahedra rotation on ionic transport in β-K3PO4 based solid electrolytes. One of the factors which indicates the existence of the “paddle-wheel” mechanism in Li2SO4 is activation energy increase and conductivity decrease when SO4 groups are substituted by tetrahedral groups which contain a heavier polyvalent cation than S6+[28,29]. Such a behavior was found for α-Li2SO4 based solid solution in Li2SO4 –Li2WO4[30], Li2SO4 –Li3PO4[31], Li2SO4 –Li3VO4[32] systems. P5+, V5+ and W6+ ions are bigger and heavier as compared with S6+ so PO4, VO4 and WO4 tetrahedra have a larger moment of inertia than SO4 in consequence of which the rate of their reorientation is smaller.
As a result, activation energy for ionic conductivity increases. As it is seen from Fig. 3, which has been plotted according to the data from [5], there is a tendency towards an activation energy rise with the growth of ionic radius of E6+. However, there is a jump-like increase of activation energy at the transition from Mo6+ to W6+, in spite of the fact that their ionic radii are almost equal. It should be mentioned that the increase of the potential barrier with the growth of ionic radius of the dopant is not typical for solid electrolytes with large alkali cation conductivity, such as K+[33], Rb and Cs. The increase of ionic radius of dopant usually leads to a decrease of activation energy as a result of the extension of migration channels and the decrease of steric hindrances [9,33]. In [5] we supposed that the dependence shown in Fig. 3 may be the result of the bond strength enhancement caused by a certain decrease of electronegativity of the dopant (according to Batsanov [34] electronegativity is equal to 2.5, 2.2, 2.2 and 2.1 for S, Cr, Mo and W respectively). It should be mentioned, however, that the cited values are too close to explain the data in Fig. 3. If we use the values of electronegativity by different scales, Mo and W even change places: 1.3 and 1.4 by Allred and Rochov [35], 2.2 and 2.4 by Pauling [36] for Mo and W, respectively. Quite a different picture is observed if we look at the dependence of activation energy in K3 − xP1 − xExO4 solid electrolytes on relative atomic mass of E6+ ion (Fig. 4). One can see that there is a gradual increase of activation energy with the mass of hexavalent ion. In the light of what has been said above, such a behavior may be explained by the decrease of the EO4 tetrahedra rotation rate with the increase of hexavalent ion mass. As a result, the contribution of “paddle wheel” mechanism to the total ionic transport decreases and the effective activation energy increases.
Fig. 2. Dependence of the ac conductivity activation energy for K2.70M0.15PO4 solid electrolytes on relative atomic mass of M.
Fig. 4. Dependence of the ac conductivity activation energy for K2.90P0.90E0.10O4 solid electrolytes on relative atomic mass of E.
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E.I. Burmakin, G.S. Shekhtman / Solid State Ionics 265 (2014) 46–48
3. Conclusion The analysis of the transport properties of the solid electrolytes based on β-K3PO4 in K3 − 2xMIIxPO4 and K3 − xP1 − xEVIxO4 systems shows that the solid electrolytes under discussion may be considered as orientation disordered phases in which the “paddle wheel” mechanism makes a significant contribution to ion transport, in addition to the usual hopping mechanism. The contribution of the “paddle wheel” mechanism to the total ionic transport depends on the rate of PO4 (EO4) tetrahedra rotation. The latter, in its turn, depends on the mass of M2+ and E6+ ions. Acknowledgment The authors gratefully acknowledge the Shared Access Centre “Composition of Compounds” for analytical support. References [1] D.N. Mosin, E.A. Marks, E.I. Burmakin, N.G. Molchanova, G.Sh. Shekhtman, Russ. J. Electrochem. 37 (2001) 863–864. [2] A.W. Kolsi, Rev. Chim. Miner. 13 (1976) 416–421. [3] T. Znamierowska, Pol. J. Chem. 53 (1979) 1415–1419. [4] T. Znamierowska, Pol. J. Chem. 55 (1981) 747–756. [5] E.I. Burmakin, D.N. Mosin, G.Sh. Shekhtman, Russ. J. Electrochem. 37 (2001) 1212–1215. [6] E.I. Burmakin, G.Sh. Shekhtman, Russ. J. Electrochem. 40 (2004) 208–211. [7] E.I. Burmakin, G.Sh. Shekhtman, Russ. J. Electrochem. 40 (2004) 820–824. [8] E.I. Burmakin, G.Sh. Shekhtman, Russ. J. Electrochem. 38 (2002) 1309–1313. [9] E.I. Burmakin, Solid Electrolytes with Alkali Ion Conductivity, Nauka, Moskow, 1992. (in Russian). [10] A.K. Ivanov-Shitz, I.V. Murin, Solid State Ionics, Vol.1, St-Petersburg University ed., St-Petersburg, 2000 (in Russian). [11] M. Avdeev, V.B. Nalbandyan, I.L. Shukaev, in: V. Kharton (Ed.), Solid State Electrochemistry: Fundamentals, Methodology and Applications, Wiley-VCH, Wenheim, 2009, pp. 227–279. [12] E.I. Burmakin, G.Sh. Shekhtman, B.D. Antonov, Electrohim. Energ. 13 (2013) 19–22.
[13] G.Sh. Shekhtman, E.I. Burmakin, XVI Russian Conference “Physical Chemistry and Electrochemistry of Molten and Solid Electrolytes”, vol.2, Ural State University ed., Ekaterinburg, 2013, p. 249, (Abstracts). [14] V.I. Voronin, Yu.S. Ponosov, I.F. Berger, N.V. Proskurnina, V.G. Zubkov, A.P. Tyutyunnik, S.N. Bushmeleva, A.M. Balagurov, D.V. Sheptyakov, E.I. Burmakin, G.Sh. Shekhtman, E.G. Vovkotrub, Inorg. Mater. 42 (2006) 908–913. [15] R. Hoppe, H.M. Seyfert, Naturforsch 28 (1974) 507–508. [16] W. Jungowska, T. Znamierowska, J. Solid State Chem. 95 (1991) 265–269. [17] A. Lunden, in: B.V.R. Chowdari, S. Radhakrishna (Eds.), Materials for Solid State Batteries, World Sci. Publ., Singapore, 1986, pp. 149–160. [18] A. Lunden, Solid State Commun. 65 (1988) 1237–1240. [19] A. Lunden, Solid State Ionics 28–30 (1988) 163–167. [20] A.S. Ulihin, N.F. Uvarov, Russ. J. Electrochem. 43 (2007) 644–647. [21] N.F. Uvarov, A.S. Ulihin, A.A. Iskakova, A.N. Medvedev, A.V. Anikeenko, Russ. J. Electrochem. 47 (2011) 404–409. [22] N.F. Uvarov, A.A. Iskakova, A.S. Ulihin, A.N. Medvedev, A.V. Anikeenko, Solid State Ionics 188 (2011) 78–82. [23] L.Z. Akhtyamova, V.I. Voronin, G.Sh. Shekhtman, E.I. Burmakin, S.S. Stroev, Materials of XII International Conference on Selected Problems of Modern Physics, Joint Institute for Nuclear Research, Publishing Department ed., Dubna, 2003, p. 47. [24] V.I. Voronin, N.V. Proskurnina, G.Sh. Shekhtman, E.I. Burmakin, S.S. Stroev, Materials Structure in Chemistry, Biology and Technology, Czech and Slovak Crystallographic Association ed., Prague, 2004, p. 192, (Abstract). [25] A. Kvist, A. Bengtzelius, in: W. van Gool (Ed.), Fast Ion Transport in Solids, North Holland Publishing Company, Amsterdam, 1973, pp. 193–199. [26] B. Heed, A. Lunden, K. Schroeder, Electrochim. Acta 22 (1977) 705–707. [27] L. Nilsson, N.H. Andersen, A. Lunden, Solid State Ionics 34 (1989) 111–119. [28] N.H. Andersen, P.W.S.K. Bandaranayake, M.A. Careem, M.A.K.L. Dissanayake, S.N. Wijasekera, N. Kaber, A. Lunden, B.-E. Mellander, L. Nilsson, J.O. Thomas, Solid State Ionics 57 (1992) 203–209. [29] A. Lunden, Solid State Ionics 68 (1994) 77–80. [30] M.A.K.L. Dissanayake, M.A. Careem, P.W.S.K. Bandaranajake, S.N. Wijasekera, Solid State Ionics 48 (1991) 277–281. [31] M. Touboul, N. Sephar, M. Quarton, Solid State Ionics 38 (1990) 225–229. [32] M. Touboul, A. Elfakir, M. Quarton, Solid State Ionics 82 (1995) 61–65. [33] E.I. Burmakin, Mater. Sci. Forum 76 (1991) 69. [34] S.S. Batsanov, Eksperimental'nye osnovy Strukturnoi Khimii, Standarty, Moskow, 1986. (in Russian). [35] A.L. Allred, E.G. Rochov, J. Inorg. Nucl. Chem. 5 (1958) 264–269. [36] M.C. Day, J. Selbin, Theoretical Inorganic Chemistry, 2nd ed. Reinhold Book Corporation, New York, Amsterdam, London, 1971. [37] R.D. Shannon, Acta Crystallogr. A32 (1976) 751–767.
Contents lists available at ScienceDirect
Solid State Ionics journal homepage: www.elsevier.com/locate/ssi
On ion transport mechanism in K+-conducting solid electrolytes based on K3PO4 E.I. Burmakin, G.Sh. Shekhtman ⁎ Institute of High Temperature Electrochemistry Urals Branch RAS, S.Kovalevskoy Street 22, 620990 Ekaterinburg, Russian Federation
a r t i c l e
i n f o
Article history: Received 14 March 2014 Received in revised form 27 June 2014 Accepted 16 July 2014 Available online xxxx Keywords: Solid electrolytes Potassium ion conductivity Potassium orthophosphate
a b s t r a c t Data on transport properties of potassium conducting solid electrolytes based on K3PO 4 in the systems K3 − 2xMxPO4 (M = Mg, Ca, Sr, Ba, Zn, Cd, Pb) and K3 − xP 1 − xE xO4 (E = S, Cr, Mo, W) have been analyzed. The results indicate that, in addition to the usual hopping mechanism, a substantial significance for ion transport in similar phases belongs to the “paddle wheel” mechanism. This mechanism is due to orientation disorder of the PO4 tetrahedra at elevated temperatures, which promotes moving K+ ions to the neighboring vacant positions. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Potassium orthophosphate K3PO4 has a rather high potassium ion conductivity at elevated temperatures, which is 5 × 10−4–5 × 10−2 S cm−1 in 400–800 °C temperature range [1]. Heterovalent substitutions which lead to potassium vacancy creation, such as 2 K+ → M2+ + VK or P5+ + K+ → E6+ + VK, are accompanied by the formation of solid solutions [2–5] whose K+-ion conductivity reaches 10−2 S cm−1 at 300 °C [5–8]. These values are among the best ones for polycrystalline potassium conducting solid electrolytes [9–11]. While analyzing the results obtained for K3 − 2xMxPO4 (M = Mg, Ca, Sr, Ba, Zn, Cd, Pb), we considered the influence of ionic radius of M2+ and the effect of complex formation at high level of doping on potassium ion transport [6,12,13]. These factors are certainly of importance for hopping ionic transport, but the analysis of experimental data as a whole shows that there exists an additional factor that influences ionic transport in such systems. 2. Results and discussion At room temperature K3PO4 is orthorhombic, space group Pnma, a = 1.12377(2), b = 0.81046(1), c = 0.59227(1) nm, z = 4 [14]. With increasing temperature, low temperature orthorhombic γ-form of K3PO4 transforms into a high temperature fcc β one, space group Fm3, a = 0.811 nm, z = 4 [15,16]. The temperature of γ ↔ β transition is 550 ± 10 °C [1,2,16]. The cubic β polymorph of potassium orthophosphate forms extensive ranges of solid solutions when 2 K → M2+ + VK or K+ + P5+ → E6+ + VK replacing mechanism is applied, and the cubic lattice in most such cases is stable down to room temperature. In this ⁎ Corresponding author. E-mail address: [email protected] (G.S. Shekhtman).
http://dx.doi.org/10.1016/j.ssi.2014.07.011 0167-2738/© 2014 Elsevier B.V. All rights reserved.
work we compared the data obtained for K3 − 2xMxPO4 (M = Mg, Ca, Sr, Ba, Zn, Cd, Pb) and K3 − xP1 − xExO4 (E = S, Cr, Mo, W) systems for samples with the same “x” value and crystal lattice (fcc β — form of K3PO4). The value of “x” in every range of systems corresponds to the samples whose composition lies within single-phase β-K3PO4 region, not too close to its boundary. For the first range of systems these requirements were met by samples with x = 0.15, for the second one — 0.10. All the values of activation energy are cited for high temperature flat region of lgσ − 1 / T dependences (400–750 °C). In the low temperature region deviations from linearity were observed in some cases, which made it difficult to define the activation energy adequately. Fig. 1 shows conductivity activation energy against M2+ ionic radius. As one can see, there is no correlation between E and r(M2+). Proceeding from this, we decided to analyze the influence of the crystal structure peculiarities of β-K3PO4 on ion transport of the solid solutions under discussion. It is well known that for a number of phases based on isolated ZO4 tetrahedra there exists orientation disordering of these tetrahedra at elevated temperatures. The best known example is Li2SO4 which was examined in detail by Lunden [17–19]. It was shown that the reorientation of SO4 tetrahedra enhances the mobility of Li+ ions and ionic conductivity by the so called “paddle-wheel” mechanism. According to “paddle-wheel” mechanism contributions to enhanced Li+ ions mobility are expected to come from two sources. One is from the rotatory motion of SO4 tetrahedra which pushes the lithium ions. The other is from the lowering of potential barrier making it easier for a vibrating Li+ ion to jump to an empty adjacent position. In such a case the usual “hopping” conductivity mechanism remains in force too, so the “paddle-wheel” is not the only mechanism but an additional one which quickens the total ionic transport and decreases effective activation energy. A similar mechanism was later proposed for the interpretation of ionic conductivity in alkali nitrates and perchlorates
E.I. Burmakin, G.S. Shekhtman / Solid State Ionics 265 (2014) 46–48
47
Fig. 1. Dependence of the ac conductivity activation energy for K2.70M0.15PO4 solid electrolytes on M2+ ionic radius. Values of ionic radii are taken from ref. [37].
Fig. 3. Dependence of the ac conductivity activation energy for K2.90P0.90E0.10O4 solid electrolytes on E6+ ionic radius. Values of ionic radii are taken from ref. [37].
[20–22]. After that we showed by high temperature neutron diffraction that the high-temperature form of Cs3PO4 may be also considered orientation-disordered or rotor phase [23,24]. As Cs3PO4 and K3PO4 are similar in structure, it can be assumed that the transport of K+ ions in β-K3PO4 based solid solutions is strongly correlated to the rotation of the PO4 tetrahedra. According to the literature data, diffusion coefficients of mono- and divalent cations in Li2SO4 are of the same order of magnitude [25]. Therefore, in orientation-disordered phases both mono- and double-charged cations are mobile [26,27], which means that in the case of K3 − 2xMxPO4 the reorientational rotatory motion of PO4 tetrahedra will push both K+ and M2+ ions to the empty adjacent positions. The rate of rotation of PO4 tetrahedra in such a case will depend on M2+ ionic mass: the higher the M2+ ionic mass, the bigger the energy barrier for M2 + pushing. As Fig. 2 shows, experimental data and the proposed model are in good agreement: there is a strong correlation between conductivity activation energy and relative atomic mass of M. The results of studying K3 − xP1 − xExO4 (E = S, Cr, Mo, W) systems [5] confirm the influence of PO4 tetrahedra rotation on ionic transport in β-K3PO4 based solid electrolytes. One of the factors which indicates the existence of the “paddle-wheel” mechanism in Li2SO4 is activation energy increase and conductivity decrease when SO4 groups are substituted by tetrahedral groups which contain a heavier polyvalent cation than S6+[28,29]. Such a behavior was found for α-Li2SO4 based solid solution in Li2SO4 –Li2WO4[30], Li2SO4 –Li3PO4[31], Li2SO4 –Li3VO4[32] systems. P5+, V5+ and W6+ ions are bigger and heavier as compared with S6+ so PO4, VO4 and WO4 tetrahedra have a larger moment of inertia than SO4 in consequence of which the rate of their reorientation is smaller.
As a result, activation energy for ionic conductivity increases. As it is seen from Fig. 3, which has been plotted according to the data from [5], there is a tendency towards an activation energy rise with the growth of ionic radius of E6+. However, there is a jump-like increase of activation energy at the transition from Mo6+ to W6+, in spite of the fact that their ionic radii are almost equal. It should be mentioned that the increase of the potential barrier with the growth of ionic radius of the dopant is not typical for solid electrolytes with large alkali cation conductivity, such as K+[33], Rb and Cs. The increase of ionic radius of dopant usually leads to a decrease of activation energy as a result of the extension of migration channels and the decrease of steric hindrances [9,33]. In [5] we supposed that the dependence shown in Fig. 3 may be the result of the bond strength enhancement caused by a certain decrease of electronegativity of the dopant (according to Batsanov [34] electronegativity is equal to 2.5, 2.2, 2.2 and 2.1 for S, Cr, Mo and W respectively). It should be mentioned, however, that the cited values are too close to explain the data in Fig. 3. If we use the values of electronegativity by different scales, Mo and W even change places: 1.3 and 1.4 by Allred and Rochov [35], 2.2 and 2.4 by Pauling [36] for Mo and W, respectively. Quite a different picture is observed if we look at the dependence of activation energy in K3 − xP1 − xExO4 solid electrolytes on relative atomic mass of E6+ ion (Fig. 4). One can see that there is a gradual increase of activation energy with the mass of hexavalent ion. In the light of what has been said above, such a behavior may be explained by the decrease of the EO4 tetrahedra rotation rate with the increase of hexavalent ion mass. As a result, the contribution of “paddle wheel” mechanism to the total ionic transport decreases and the effective activation energy increases.
Fig. 2. Dependence of the ac conductivity activation energy for K2.70M0.15PO4 solid electrolytes on relative atomic mass of M.
Fig. 4. Dependence of the ac conductivity activation energy for K2.90P0.90E0.10O4 solid electrolytes on relative atomic mass of E.
48
E.I. Burmakin, G.S. Shekhtman / Solid State Ionics 265 (2014) 46–48
3. Conclusion The analysis of the transport properties of the solid electrolytes based on β-K3PO4 in K3 − 2xMIIxPO4 and K3 − xP1 − xEVIxO4 systems shows that the solid electrolytes under discussion may be considered as orientation disordered phases in which the “paddle wheel” mechanism makes a significant contribution to ion transport, in addition to the usual hopping mechanism. The contribution of the “paddle wheel” mechanism to the total ionic transport depends on the rate of PO4 (EO4) tetrahedra rotation. The latter, in its turn, depends on the mass of M2+ and E6+ ions. Acknowledgment The authors gratefully acknowledge the Shared Access Centre “Composition of Compounds” for analytical support. References [1] D.N. Mosin, E.A. Marks, E.I. Burmakin, N.G. Molchanova, G.Sh. Shekhtman, Russ. J. Electrochem. 37 (2001) 863–864. [2] A.W. Kolsi, Rev. Chim. Miner. 13 (1976) 416–421. [3] T. Znamierowska, Pol. J. Chem. 53 (1979) 1415–1419. [4] T. Znamierowska, Pol. J. Chem. 55 (1981) 747–756. [5] E.I. Burmakin, D.N. Mosin, G.Sh. Shekhtman, Russ. J. Electrochem. 37 (2001) 1212–1215. [6] E.I. Burmakin, G.Sh. Shekhtman, Russ. J. Electrochem. 40 (2004) 208–211. [7] E.I. Burmakin, G.Sh. Shekhtman, Russ. J. Electrochem. 40 (2004) 820–824. [8] E.I. Burmakin, G.Sh. Shekhtman, Russ. J. Electrochem. 38 (2002) 1309–1313. [9] E.I. Burmakin, Solid Electrolytes with Alkali Ion Conductivity, Nauka, Moskow, 1992. (in Russian). [10] A.K. Ivanov-Shitz, I.V. Murin, Solid State Ionics, Vol.1, St-Petersburg University ed., St-Petersburg, 2000 (in Russian). [11] M. Avdeev, V.B. Nalbandyan, I.L. Shukaev, in: V. Kharton (Ed.), Solid State Electrochemistry: Fundamentals, Methodology and Applications, Wiley-VCH, Wenheim, 2009, pp. 227–279. [12] E.I. Burmakin, G.Sh. Shekhtman, B.D. Antonov, Electrohim. Energ. 13 (2013) 19–22.
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