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Crystal structure of Li4ZnTeO6 and revision of Li3Cu2SbO6
Journal of Solid State Chemistry 199 (2013) 62–65
Contents lists available at SciVerse ScienceDirect
Journal of Solid State Chemistry journal homepage: www.elsevier.com/locate/jssc
Crystal structure of Li4ZnTeO6 and revision of Li3Cu2SbO6 V.B. Nalbandyan a,n, M. Avdeev b, M.A. Evstigneeva a a b
Southern Federal University, 7 ul, Zorge, Rostov-na-Donu 344090, Russian Federation Bragg Institute, ANSTO, Kirrawee DC NSW, Australia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 September 2012 Received in revised form 14 November 2012 Accepted 25 November 2012 Available online 3 December 2012
Li4ZnTeO6 has been prepared by solid-state reactions and characterized by powder X-ray and neutron ˚ b ¼ 110.783(3)1. The diffraction. It is monoclinic, C2/m, a ¼5.2114(3), b ¼ 8.9288(4), c ¼ 5.1768(3) A, material is structurally analogous to Li3Zn2SbO6 with LiTe substitution for ZnSb. The structure is based on honeycomb [(Li,Zn)2TeO6]3 layers interleaved with Li þ layers. Minor substitution of Zn in Li layers was detected. It is shown that Li3Cu2SbO6 known as C2/c actually belongs to the same C2/m type with halved unit cell volume. & 2012 Elsevier Inc. All rights reserved.
Keywords: Tellurate Antimonate Layered structure Rietveld Neutron diffraction X-ray diffraction
1. Introduction Mixed oxides of the Ax(M,L)O2 formula type based on brucitelike octahedral (M,L)O6/3 layers with an alkali cation A in the interlayer constitute a wide class of compounds with diverse properties. LiCoO2 and its substituted analogs are electrode materials of the Li–ion batteries [1]. NaxCoO2 bronzes are efficient thermoelectric materials [2] and superconductors when hydrated [3]. Very high alkali-cation conductivity is exhibited by Kx(InxM1 x)O2 (MQSn, Zr, Hf) [4], Kx(Sn1 yMy)O2 (MQMg, Ca, Zn, Li) [5,6], Kx(Sb1 yMy)O2 (MQNi, Mg) [7], Nax(Ti1 yMy)O2 (MQFe, Mg, Ni, Co, Cr, Li) [8–13], Nax(Sb1 yMy)O2 (MQFe, Ni, Cr) [14–16], Na2M2TeO6 (MQMg, Co, Ni, Zn) [17] and Na2LiFeTeO6 [18]. Depending on the stacking mode of the octahedral layers, there are several polytypes designated O3, P2, P3, etc., where O and P stand for octahedral and trigonal-prismatic coordination of the A ions, respectively, and the digit indicates number of brucitelike layers in the hexagonal unit cell [19]. In most cases where two heterovalent cations M and L are present, their distribution is apparently random, resulting in a ˚ However, in those short hexagonal lattice parameter of ca. 3 A. cases where M and L are in a ratio of 1:2 and differ significantly in size and/or oxidation state, a honeycomb-like superlattice ordering appears. Such ordering of paramagnetic cations results in unusual magnetic properties and attracts much attention [20–28].
n
Corresponding author. Fax: þ7 863 297 5151. E-mail address: [email protected] (V.B. Nalbandyan).
0022-4596/$ - see front matter & 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jssc.2012.11.027
Within the P2 family, three honeycomb-like superlattices are found with space groups P63/mcm [17,29], P6322 [17,22,29], and P212121 [18]. Within the most numerous O3 family, there are also three stacking variants of honeycomb-like layers with space groups C2/m, C2/c and P3112. However, the monoclinic phases usually do not show peak splitting in their diffraction patterns and may be easily indexed as trigonal [15,30]. Li3M2SbO6 with MQZn [31], Ni [26] and Co [32], Li3M2BiO6 with MQZn [31] and Ni [27], Na2Cu2TeO6 [20], Na3Cu2SbO6 [30] and many other A3M2LO6 compounds (including those with LQA, i.e. A2MO3 such as Na2IrO3 [25]) belong to the C2/m group. Although Li3Cu2SbO6 was originally described as C2/c [33], our analysis has shown that those experimental data obey C2/m with halved unit cell volume (see Table 1 and the pdf file in Supplementary data). The three Cu compounds differ from others by strong Jahn–Teller distortion of the CuO6 octahedra thus prohibiting the trigonal indexing. Li4FeSbO6 [28] and Li4MgReO6 [34] also belong to this group with apparently random mixing of Li þ and Fe3 þ or Mg2 þ on Zn2 þ sites of Li3Zn2SbO6 although local ordering is highly probable [28]. Layered nature of the brucite-related family enables relatively easy ion-exchange substitution of the interlayer A cations [6,14,15,26,27,29,32], a soft chemical route to phases that often cannot be prepared by direct synthesis. In continuation of our search for mixed alkali and transition metal antimonates [7,14–16,26,28,30,32,35–37] and tellurates [17,18,37,38], we started structural studies of several A4MTeO6 compounds (AQLi, Na; MQCo, Ni, Zn). Here, Li4ZnTeO6 will be structurally characterized. It shows a profound analogy with the
V.B. Nalbandyan et al. / Journal of Solid State Chemistry 199 (2013) 62–65
63
Table 1 Comparison of different indexing variants for the powder pattern of Li3Cu2SbO6 and corresponding figures of merit (FoM). Source of the data
Space group
˚ a (A)
˚ b (A)
˚ c (A)
b (1)
V (A˚ 3)
FoM [42]
PDF 00-48-68 (experimental) PDF 01-88-478 (calculated [33]) PDF 00-48-68 reindexed
C2/c C2/c C2/m
5.4644(5) 5.4659(1) 5.4655(7)
8.7215(8) 8.7272(2) 8.7216(8)
9.7760(9) 9.7807(3) 5.3845(7)
95.095(8) 95.080(2) 115.270(5)
464.1 464.7 232.1
35 58
Fig. 2. Powder neutron diffraction pattern of Li4ZnTeO6 crosses, experimental data; line, calculated intensity; vertical bars, Bragg positions; line in the bottom, difference profile. Fig. 1. Powder XRD pattern of Li4ZnTeO6.
family of Li3M2SbO6 compounds and serves as a diamagnetic model for heat capacity studies of magnetic phase transitions in Li4FeSbO6 [28] and Li4MTeO6 (MQCo, Ni). After the initial submission of this paper, a communication appeared reporting a series of Li4MTeO6 (MQCo, Ni, Cu, Zn) and Li4MSbO6 (MQAl, Cr, Fe, Ga) compounds ‘‘with innumerable prospects of properties and applications’’ [39], of which conductivity and magnetization were reported for the Co compound as well as Ag þ ion exchange. The lattice parameters for MQCo, Ni, Zn, and Fe agree with ours within 0.2% but structural data are only reported for MQCu and Co.
2. Experimental Reagent-grade lithium carbonate, zinc oxide and tellurium dioxide were dried at 150 1C and stored in a desiccator. Weighed portions of the reagents were mixed thoroughly with a mortar and pestle, pressed into thin pellets and heat-treated in air for 2 h at 600 1C to expel carbon dioxide and enable oxidation of Te(4þ) to Te(6þ). Then the pellets were ground, part of the powder pressed again, covered with the rest (sacrificial) powder to prevent volatilization of components and calcined at 850 1C two times for 2 h each with intermediate grinding and pressing. XRD phase analysis was done using an ARL X’TRA diffractometer equipped with a solid-state Si(Li) detector. Corundum (NIST SRM 676) served as an internal standard for lattice parameter refinement. Neutron diffraction measurements were performed with the Echidna diffractometer at the OPAL facility of the Australian Nuclear Science and Technology Organization with ˚ For Rietveld refinement, neutron wavelengths of 1.6215 A. GSASþEXPGUI suite [40,41] was used.
3. Results and discussion The XRD pattern of the nominal Li4ZnTeO6 (Fig. 1) was completely indexed on the monoclinic unit cell of the Li3Zn2SbO6 type with figure of merit [42] of 22 and submitted for inclusion into the Powder Diffraction File (PDF) of the International Centre for Diffraction Data. From the systematic absences, only C centering could be deduced with three possible space groups: C2, Cm and C2/m. Space group C2/m was selected by analogy with Li3Zn2SbO6 [31] and confirmed by the Rietveld analysis. The structural study was based on the neutron diffraction data (Fig. 2) that permit more precise location of light elements, Li and O. Crystallographic data, refinement details, atomic parameters and selected interatomic distances are listed in Tables 2–4 and the crystal structure is illustrated in Fig. 3. Besides Li/Zn mixing on Zn sites of the Li3Zn2SbO6 prototype, partial substitution of Zn in the Li layer was also allowed, and small fraction of Zn was actually found in one of the two sites in the Li layer. Occupancies of the two Zn/Li sites were refined independently and resulted in the composition that differs from the nominal one only within experimental uncertainties: Li4.025(17)Zn0.975(17)TeO6. Average interatomic distances are in good agreement with corresponding sums of ionic radii (Table 4). The refined structure has been submitted for inclusion into the Inorganic Crystal Structure Database (ICSD), number 425155. The same structure type is found for Li4NiTeO6, Li4CoTeO6 (both are now under study) and confirmed by the XRD Rietveld refinement for Li4FeSbO6 [28] with apparently random mixing of Li þ /Fe3 þ or Li þ /M2 þ on Zn sites of Li3Zn2SbO6. Ordering of the two cations on these sites would be incompatible with the mirror plane resulting in space group C2, but refinement of the C2 model for Li4FeSbO6 resulted in essentially identical occupancies of the two sites, and the C2/m group was retained [28]. Since Li þ is more similar to Zn2 þ than to Fe3 þ in both size and charge, Li/Zn ¨ ordering was not attempted. However, Mossbauer spectra indicate that most of Fe3 þ in Li4FeSbO6 have highly symmetrical
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V.B. Nalbandyan et al. / Journal of Solid State Chemistry 199 (2013) 62–65
Table 2 Crystallographic data and details of structure refinement of Li4ZnTeO6. Crystal system Space group
Monoclinic C2/m
Radiation
Neutrons
Lattice parameters
˚ a (A) ˚ b (A) ˚ c (A) b (1) V (A˚ 3)
5.2114(3)
5.215(3)
8.9288(4)
8.932(2)
5.1768(3)
5.179(3)
110.783(3) 225.21
110.81(3) 225.50
Z Density (calc.) (g/cm3) 2Y range (1) Number of data points Number of hkl’s Number of parameters Agreement factors
CuKa
2 4.67
Rwp Rp
w2
10–155 2900 225 36 0.0624 0.0485 3.78
Fig. 3. Polyhedral presentation of the crystal structure of Li4ZnTeO6, Dark gray octahedra, TeO6; light octahedra, (Li0.58Zn0.42)O6; white balls, Li; gray balls, Li0.87Zn0.13.
Table 3 Atomic coordinates, thermal parameters and site occupancies in Li4ZnTeO6. Atom
Site x
y
z
Uiso/Ueq (A˚ 2) p
Te (Li1 pZnp)1 Li2 (Li1 pZnp)3 O1 O2
2a 4g 4h 2d 4i 8j
0 0.3413(16) 0.1707(16) 0.5 0 0.1525(2)
0 0 0.5 0.5 0.2235(7) 0.2340(5)
0.0161(11) 0.011(3) 0.0329a 0.0329a 0.0151(7) 0.0085(4)
0 0 0 0 0.7716(7) 0.2312(4)
Crystallographic information file (CIF) for Li4ZnTeO6 and a pdf document describing reindexing and revised Li3Cu2SbO6 structure are available free of charge from http://www.sciencedirect.com.
0.422(5) 0.131(7)
a
Refined anisotropically under constraint of equal Uij for 4 h and 2d sites: U11 ¼ 0.026(5), U22 ¼0.060(6), U33 ¼ 0.015(4), U13 ¼0.010(3) A˚ 2.
Acknowledgments V.B.N. and M.A.E. acknowledge support from the International Centre for Diffraction Data (Grant-in-aid 00-15) and Russian Foundation for Basic Research (Grant 11-03-01101-a).
Appendix A. Supporting information
Table 4 ˚ in Li4ZnTeO6. Important interatomic distances (A) Te–O2 Te–O1 Average Sum of radii [43] (Li,Zn)1–O1 (Li,Zn)1–O2 (Li,Zn)1–O2 Average Sum of radii [43]
Supplementary data
1.933(2) 4 1.932(4) 2 1.933 1.96 2.046(10) 2 2.153(3) 2 2.174(11) 2 2.125 2.15
Li2–O1 Li2–O2 Li2–O2 Average Sum of radii [20] (Li,Zn)3–O2 (Li,Zn)3–O1 Average Sum of radii [20]
2.133(3) 2 2.140(10) 2 2.232(10) 2 2.168 2.16 2.084(2) 4 2.343(4) 2 2.170 2.16
environment [28]. It is, therefore, supposed that each individual layer in Li4FeSbO6 and Li4MTeO6 (MQZn, Co, Ni, Cu) may be essentially ordered according to the C2 model but their stacking is disordered resulting in the apparent C2/m symmetry. The stacking disorder is manifested in elevated sloping background near strongest superlattice reflections at 2Y ¼19–251 (Fig. 1), typical of brucite-related superlattices [14,15,26–29].
4. Conclusions The powder diffraction study has shown a profound structural analogy between the known monoclinic Li3M2SbO6 (MQCo, Ni, Cu, Zn), Li4FeSbO6 and new Li4ZnTeO6. The analogy is based on close similarity of ionic sizes and oxidation states between Li þ and M2 þ , Sb5 þ and Te6 þ . In addition, Te6 þ and Sb5 þ are isoelectronic. Li4MgTeO6 and Li3Mg2SbO6 have not been reported so far but are expected to have structures of the same type.
Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.jssc.2012.11.027.
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[31] C. Greaves, S.M.A. Katib, Mater. Res. Bull. 25 (1990) 1175–1182. [32] Powder Diffraction File (PDF), International Centre for Diffraction Data, 12 Campus Blvd, Newtown Square, PA, USA, 19073: PDF Card 00-058-637. [33] J.M.S. Skakle, M.A. Castellanos R., S.T. Tovar, A.R. West, J. Solid State Chem. 131 (1997) 115–120. [34] M. Bieringer, J.E. Greedan, G.M. Luke, Phys. Rev. B 62 (2000) 6521–6528. [35] O.A. Smirnova, M. Avdeev, V.B. Nalbandyan, V.V. Kharton, F.M.B. Marques, Mater. Res. Bull. 41 (2006) 1056–1062. [36] O.A. Smirnova, J. Rocha, V.B. Nalbandyan, V.V. Kharton, F.M.B. Marques, Solid State Ionics 178 (2007) 1360–1365. [37] Powder Diffraction File (PDF), International Centre for Diffraction Data, 12 Campus Blvd, Newtown Square, PA, USA, 19073: PDF Cards 00-58-628, 00058-636, 00-058-0638, 00-58-770, 00-59-386, 00-59-443, 00-59-444, 00-59-445, 00-59-538, 00-61-718. [38] A.A. Pospelov, V.B. Nalbandyan, E.I. Serikova, B.S. Medvedev, M.A. Evstigneeva, E.V. Ni, V.V. Lukov, Solid State Sci. 13 (2011) 1899–2066. [39] V. Kumar, N. Bhardwaj, N. Tomar, V. Thakral, S. Uma, Inorg. Chem. 51 (2012) 10471–10473. [40] A.C. Larson, R.B. Von Dreele, General Structure Analysis System (GSAS), Los Alamos National Laboratory Report LAUR 86-748, 2004. [41] B.H. Toby, J. Appl. Cryst. 34 (2001) 210–213. [42] G.S. Smith, R.L. Snyder, J. Appl. Cryst. 12 (1979) 60–65. [43] R.D. Shannon, Acta Cryst. A32 (1976) 751–767.
Contents lists available at SciVerse ScienceDirect
Journal of Solid State Chemistry journal homepage: www.elsevier.com/locate/jssc
Crystal structure of Li4ZnTeO6 and revision of Li3Cu2SbO6 V.B. Nalbandyan a,n, M. Avdeev b, M.A. Evstigneeva a a b
Southern Federal University, 7 ul, Zorge, Rostov-na-Donu 344090, Russian Federation Bragg Institute, ANSTO, Kirrawee DC NSW, Australia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 September 2012 Received in revised form 14 November 2012 Accepted 25 November 2012 Available online 3 December 2012
Li4ZnTeO6 has been prepared by solid-state reactions and characterized by powder X-ray and neutron ˚ b ¼ 110.783(3)1. The diffraction. It is monoclinic, C2/m, a ¼5.2114(3), b ¼ 8.9288(4), c ¼ 5.1768(3) A, material is structurally analogous to Li3Zn2SbO6 with LiTe substitution for ZnSb. The structure is based on honeycomb [(Li,Zn)2TeO6]3 layers interleaved with Li þ layers. Minor substitution of Zn in Li layers was detected. It is shown that Li3Cu2SbO6 known as C2/c actually belongs to the same C2/m type with halved unit cell volume. & 2012 Elsevier Inc. All rights reserved.
Keywords: Tellurate Antimonate Layered structure Rietveld Neutron diffraction X-ray diffraction
1. Introduction Mixed oxides of the Ax(M,L)O2 formula type based on brucitelike octahedral (M,L)O6/3 layers with an alkali cation A in the interlayer constitute a wide class of compounds with diverse properties. LiCoO2 and its substituted analogs are electrode materials of the Li–ion batteries [1]. NaxCoO2 bronzes are efficient thermoelectric materials [2] and superconductors when hydrated [3]. Very high alkali-cation conductivity is exhibited by Kx(InxM1 x)O2 (MQSn, Zr, Hf) [4], Kx(Sn1 yMy)O2 (MQMg, Ca, Zn, Li) [5,6], Kx(Sb1 yMy)O2 (MQNi, Mg) [7], Nax(Ti1 yMy)O2 (MQFe, Mg, Ni, Co, Cr, Li) [8–13], Nax(Sb1 yMy)O2 (MQFe, Ni, Cr) [14–16], Na2M2TeO6 (MQMg, Co, Ni, Zn) [17] and Na2LiFeTeO6 [18]. Depending on the stacking mode of the octahedral layers, there are several polytypes designated O3, P2, P3, etc., where O and P stand for octahedral and trigonal-prismatic coordination of the A ions, respectively, and the digit indicates number of brucitelike layers in the hexagonal unit cell [19]. In most cases where two heterovalent cations M and L are present, their distribution is apparently random, resulting in a ˚ However, in those short hexagonal lattice parameter of ca. 3 A. cases where M and L are in a ratio of 1:2 and differ significantly in size and/or oxidation state, a honeycomb-like superlattice ordering appears. Such ordering of paramagnetic cations results in unusual magnetic properties and attracts much attention [20–28].
n
Corresponding author. Fax: þ7 863 297 5151. E-mail address: [email protected] (V.B. Nalbandyan).
0022-4596/$ - see front matter & 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jssc.2012.11.027
Within the P2 family, three honeycomb-like superlattices are found with space groups P63/mcm [17,29], P6322 [17,22,29], and P212121 [18]. Within the most numerous O3 family, there are also three stacking variants of honeycomb-like layers with space groups C2/m, C2/c and P3112. However, the monoclinic phases usually do not show peak splitting in their diffraction patterns and may be easily indexed as trigonal [15,30]. Li3M2SbO6 with MQZn [31], Ni [26] and Co [32], Li3M2BiO6 with MQZn [31] and Ni [27], Na2Cu2TeO6 [20], Na3Cu2SbO6 [30] and many other A3M2LO6 compounds (including those with LQA, i.e. A2MO3 such as Na2IrO3 [25]) belong to the C2/m group. Although Li3Cu2SbO6 was originally described as C2/c [33], our analysis has shown that those experimental data obey C2/m with halved unit cell volume (see Table 1 and the pdf file in Supplementary data). The three Cu compounds differ from others by strong Jahn–Teller distortion of the CuO6 octahedra thus prohibiting the trigonal indexing. Li4FeSbO6 [28] and Li4MgReO6 [34] also belong to this group with apparently random mixing of Li þ and Fe3 þ or Mg2 þ on Zn2 þ sites of Li3Zn2SbO6 although local ordering is highly probable [28]. Layered nature of the brucite-related family enables relatively easy ion-exchange substitution of the interlayer A cations [6,14,15,26,27,29,32], a soft chemical route to phases that often cannot be prepared by direct synthesis. In continuation of our search for mixed alkali and transition metal antimonates [7,14–16,26,28,30,32,35–37] and tellurates [17,18,37,38], we started structural studies of several A4MTeO6 compounds (AQLi, Na; MQCo, Ni, Zn). Here, Li4ZnTeO6 will be structurally characterized. It shows a profound analogy with the
V.B. Nalbandyan et al. / Journal of Solid State Chemistry 199 (2013) 62–65
63
Table 1 Comparison of different indexing variants for the powder pattern of Li3Cu2SbO6 and corresponding figures of merit (FoM). Source of the data
Space group
˚ a (A)
˚ b (A)
˚ c (A)
b (1)
V (A˚ 3)
FoM [42]
PDF 00-48-68 (experimental) PDF 01-88-478 (calculated [33]) PDF 00-48-68 reindexed
C2/c C2/c C2/m
5.4644(5) 5.4659(1) 5.4655(7)
8.7215(8) 8.7272(2) 8.7216(8)
9.7760(9) 9.7807(3) 5.3845(7)
95.095(8) 95.080(2) 115.270(5)
464.1 464.7 232.1
35 58
Fig. 2. Powder neutron diffraction pattern of Li4ZnTeO6 crosses, experimental data; line, calculated intensity; vertical bars, Bragg positions; line in the bottom, difference profile. Fig. 1. Powder XRD pattern of Li4ZnTeO6.
family of Li3M2SbO6 compounds and serves as a diamagnetic model for heat capacity studies of magnetic phase transitions in Li4FeSbO6 [28] and Li4MTeO6 (MQCo, Ni). After the initial submission of this paper, a communication appeared reporting a series of Li4MTeO6 (MQCo, Ni, Cu, Zn) and Li4MSbO6 (MQAl, Cr, Fe, Ga) compounds ‘‘with innumerable prospects of properties and applications’’ [39], of which conductivity and magnetization were reported for the Co compound as well as Ag þ ion exchange. The lattice parameters for MQCo, Ni, Zn, and Fe agree with ours within 0.2% but structural data are only reported for MQCu and Co.
2. Experimental Reagent-grade lithium carbonate, zinc oxide and tellurium dioxide were dried at 150 1C and stored in a desiccator. Weighed portions of the reagents were mixed thoroughly with a mortar and pestle, pressed into thin pellets and heat-treated in air for 2 h at 600 1C to expel carbon dioxide and enable oxidation of Te(4þ) to Te(6þ). Then the pellets were ground, part of the powder pressed again, covered with the rest (sacrificial) powder to prevent volatilization of components and calcined at 850 1C two times for 2 h each with intermediate grinding and pressing. XRD phase analysis was done using an ARL X’TRA diffractometer equipped with a solid-state Si(Li) detector. Corundum (NIST SRM 676) served as an internal standard for lattice parameter refinement. Neutron diffraction measurements were performed with the Echidna diffractometer at the OPAL facility of the Australian Nuclear Science and Technology Organization with ˚ For Rietveld refinement, neutron wavelengths of 1.6215 A. GSASþEXPGUI suite [40,41] was used.
3. Results and discussion The XRD pattern of the nominal Li4ZnTeO6 (Fig. 1) was completely indexed on the monoclinic unit cell of the Li3Zn2SbO6 type with figure of merit [42] of 22 and submitted for inclusion into the Powder Diffraction File (PDF) of the International Centre for Diffraction Data. From the systematic absences, only C centering could be deduced with three possible space groups: C2, Cm and C2/m. Space group C2/m was selected by analogy with Li3Zn2SbO6 [31] and confirmed by the Rietveld analysis. The structural study was based on the neutron diffraction data (Fig. 2) that permit more precise location of light elements, Li and O. Crystallographic data, refinement details, atomic parameters and selected interatomic distances are listed in Tables 2–4 and the crystal structure is illustrated in Fig. 3. Besides Li/Zn mixing on Zn sites of the Li3Zn2SbO6 prototype, partial substitution of Zn in the Li layer was also allowed, and small fraction of Zn was actually found in one of the two sites in the Li layer. Occupancies of the two Zn/Li sites were refined independently and resulted in the composition that differs from the nominal one only within experimental uncertainties: Li4.025(17)Zn0.975(17)TeO6. Average interatomic distances are in good agreement with corresponding sums of ionic radii (Table 4). The refined structure has been submitted for inclusion into the Inorganic Crystal Structure Database (ICSD), number 425155. The same structure type is found for Li4NiTeO6, Li4CoTeO6 (both are now under study) and confirmed by the XRD Rietveld refinement for Li4FeSbO6 [28] with apparently random mixing of Li þ /Fe3 þ or Li þ /M2 þ on Zn sites of Li3Zn2SbO6. Ordering of the two cations on these sites would be incompatible with the mirror plane resulting in space group C2, but refinement of the C2 model for Li4FeSbO6 resulted in essentially identical occupancies of the two sites, and the C2/m group was retained [28]. Since Li þ is more similar to Zn2 þ than to Fe3 þ in both size and charge, Li/Zn ¨ ordering was not attempted. However, Mossbauer spectra indicate that most of Fe3 þ in Li4FeSbO6 have highly symmetrical
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V.B. Nalbandyan et al. / Journal of Solid State Chemistry 199 (2013) 62–65
Table 2 Crystallographic data and details of structure refinement of Li4ZnTeO6. Crystal system Space group
Monoclinic C2/m
Radiation
Neutrons
Lattice parameters
˚ a (A) ˚ b (A) ˚ c (A) b (1) V (A˚ 3)
5.2114(3)
5.215(3)
8.9288(4)
8.932(2)
5.1768(3)
5.179(3)
110.783(3) 225.21
110.81(3) 225.50
Z Density (calc.) (g/cm3) 2Y range (1) Number of data points Number of hkl’s Number of parameters Agreement factors
CuKa
2 4.67
Rwp Rp
w2
10–155 2900 225 36 0.0624 0.0485 3.78
Fig. 3. Polyhedral presentation of the crystal structure of Li4ZnTeO6, Dark gray octahedra, TeO6; light octahedra, (Li0.58Zn0.42)O6; white balls, Li; gray balls, Li0.87Zn0.13.
Table 3 Atomic coordinates, thermal parameters and site occupancies in Li4ZnTeO6. Atom
Site x
y
z
Uiso/Ueq (A˚ 2) p
Te (Li1 pZnp)1 Li2 (Li1 pZnp)3 O1 O2
2a 4g 4h 2d 4i 8j
0 0.3413(16) 0.1707(16) 0.5 0 0.1525(2)
0 0 0.5 0.5 0.2235(7) 0.2340(5)
0.0161(11) 0.011(3) 0.0329a 0.0329a 0.0151(7) 0.0085(4)
0 0 0 0 0.7716(7) 0.2312(4)
Crystallographic information file (CIF) for Li4ZnTeO6 and a pdf document describing reindexing and revised Li3Cu2SbO6 structure are available free of charge from http://www.sciencedirect.com.
0.422(5) 0.131(7)
a
Refined anisotropically under constraint of equal Uij for 4 h and 2d sites: U11 ¼ 0.026(5), U22 ¼0.060(6), U33 ¼ 0.015(4), U13 ¼0.010(3) A˚ 2.
Acknowledgments V.B.N. and M.A.E. acknowledge support from the International Centre for Diffraction Data (Grant-in-aid 00-15) and Russian Foundation for Basic Research (Grant 11-03-01101-a).
Appendix A. Supporting information
Table 4 ˚ in Li4ZnTeO6. Important interatomic distances (A) Te–O2 Te–O1 Average Sum of radii [43] (Li,Zn)1–O1 (Li,Zn)1–O2 (Li,Zn)1–O2 Average Sum of radii [43]
Supplementary data
1.933(2) 4 1.932(4) 2 1.933 1.96 2.046(10) 2 2.153(3) 2 2.174(11) 2 2.125 2.15
Li2–O1 Li2–O2 Li2–O2 Average Sum of radii [20] (Li,Zn)3–O2 (Li,Zn)3–O1 Average Sum of radii [20]
2.133(3) 2 2.140(10) 2 2.232(10) 2 2.168 2.16 2.084(2) 4 2.343(4) 2 2.170 2.16
environment [28]. It is, therefore, supposed that each individual layer in Li4FeSbO6 and Li4MTeO6 (MQZn, Co, Ni, Cu) may be essentially ordered according to the C2 model but their stacking is disordered resulting in the apparent C2/m symmetry. The stacking disorder is manifested in elevated sloping background near strongest superlattice reflections at 2Y ¼19–251 (Fig. 1), typical of brucite-related superlattices [14,15,26–29].
4. Conclusions The powder diffraction study has shown a profound structural analogy between the known monoclinic Li3M2SbO6 (MQCo, Ni, Cu, Zn), Li4FeSbO6 and new Li4ZnTeO6. The analogy is based on close similarity of ionic sizes and oxidation states between Li þ and M2 þ , Sb5 þ and Te6 þ . In addition, Te6 þ and Sb5 þ are isoelectronic. Li4MgTeO6 and Li3Mg2SbO6 have not been reported so far but are expected to have structures of the same type.
Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.jssc.2012.11.027.
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