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Tetrahedral structure in LiKSO4 crystals studied by 7Li and 39K NMR
Journal of Physics and Chemistry of Solids 62 (2001) 881±885
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Tetrahedral structure in LiKSO4 crystals studied by 7Li and 39 K NMR Ae Ran Lim a,*, Se-Young Jeong b b
a Department of Physics, Jeonju University, Jeonju 560-759, South Korea Department of Physics, Pusan National University, Pusan 609-735, South Korea
Received 9 March 2000; accepted 20 June 2000
Abstract The 7Li and 39K nuclear magnetic resonances in a LiKSO4 single crystal grown by the slow evaporation method were investigated by employing an NMR spectrometer. From the experimental data, the quadrupole coupling constant and asymmetry parameter were determined at room temperature. The principal axes corresponding to the largest principal value of the 7 Li and 39K EFG tensors were parallel to the hexagonal c-axis. This direction was determined to be the Z-axis of the EFG tensor. The EFG tensor of 7Li and 39K was found to be non-axially symmetric; the lithium ion is surrounded by oxygen atoms located at a slightly distorted tetrahedron, and the resultant coordinating potassium ion was enclosed by the oxygen atoms located at nine distorted tetrahedra. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: B. Crystal growth; D. Crystal structure; D. Nuclear magnetic resonance (NMR)
1. Introduction The search for LiKSO4 crystals having excellent optical quality has been extensive, and much has been reported about their physical properties. In spite of the many experiments, however, the nature of the structural phase transitions in LiKSO4 is still not well understood. LiKSO4 exhibits a rich variety of phase transitions in the temperature range 10 to 1000 K. The results of dielectric studies [1±4], EPR [5±8], optical properties [9±12], and Raman scattering measurements [13±16] for the phase transitions are not consistent. The structure of LiKSO4 at room temperature is hexagonal with space group P63 C66 and two formula units per cell [17]. It consists of alternating stacked SO4 and LiO4 tetrahedra with common oxygen tops. The K 1 ions lie on the hexagonal axis and are surrounded by nine oxygens. Topic et al. [18] have made a 39K NMR analysis of LiKSO4 at room temperature. According to their results, the rotation pattern in the ab-plane was angle independent, while the rotation patterns in the ac- and bc-planes were angle dependent. From these results, it was determined that the quadrupole * Corresponding author. Tel.: 182-63-220-2514; fax: 182-63220-2362. E-mail address: [email protected] (A.R. Lim).
coupling constant e 2qQ/h 1.27 MHz, asymmetry parameter h 0, and the principal axis corresponding to the largest principal value was parallel to the hexagonal c-axis. Also, the 7Li NMR results reported by Meng et al. [19] showed a quadrupole coupling constant e 2qQ/h 35.8 kHz and asymmetry parameter h 0. In both these studies, the electric ®eld gradient tensors of 7Li and 39K NMR were axially symmetric. However, the asymmetry parameter in LiKSO4 crystals studied by the two groups above was not consistent with the crystal structure of a slightly distorted LiO4 tetrahedron [20]. Our present work deals with the 7Li and 39K NMR in a LiKSO4 single crystal grown by the slow evaporation method. The quadrupole coupling constant, e 2qQ/h, and asymmetry parameter, h , of 7Li and 39K NMR in a LiKSO4 single crystal were analyzed through experimental data obtained with a pulse NMR spectrometer. We herein examine the crystal structure of LiKSO4 crystals through the NMR of 7Li and 39K nuclei.
2. Crystal structure LiKSO4 (lithium potassium sulfate) crystals are hexagonal with two molecular formula units per unit cell. The Ê lattice parameters of the hexagonal cell are a 5.147 A
0022-3697/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S 0022-369 7(00)00244-4
882
A.R. Lim, S.-Y. Jeong / Journal of Physics and Chemistry of Solids 62 (2001) 881±885
Fig. 1. (a) The hexagonal structure and (b) the projection in the (0001) plane of a LiKSO4 single crystal at room temperature.
Ê at room temperature [21]. The hexagonal and c 8.633 A structure and the projection in the (0001) plane of LiKSO4 single crystals are shown in Fig. 1(a) and (b), respectively. The SO4 and LiO4 tetrahedra form an ordered, three dimensional framework structure characterized by six-membered rings of three LiO4 and three SO4 tetrahedra. The apices of the three LiO4 tetrahedra point in the opposite direction from those of the three SO4 tetrahedra. The K atoms occupy positions on the hexagonal c-axis. They are coordinated by nine oxygens. The bond lengths for Li±O and K±O are listed in Table 1 [20].
Nuclear magnetic resonance signals of 7Li and 39K NMR in a LiKSO4 single crystal were measured using Bruker MSL 200 MHz NMR and DSX 400 MHz NMR spectrometer at the Korea Basic Science Institute. The static magnetic ®eld was 4.7 and 9.4 T, and the central radio frequency was set at v 0/2p 77.777 MHz for the 7Li nucleus and v 0/2p 18.676 MHz for the 29K nucleus.
3. Experimental procedure
H HZ 1 HQ 2g"B0 ´I 1 e2 qQ=4I 2I 2 1{3Iz2 2 I I
Single crystals of LiKSO4 were grown by slow evaporation from an aqueous solution at 328C. The solution contained equimolar amounts of Li2SO4.H2O and K2SO4. The colorless single crystals prepared were about 5 £ 5 £ 10 mm 3. The orientations of the crystal were determined by the X-ray Laue method. The angular dependence of the NMR spectra was measured on the crystallographic ab-, bc-, and ca-planes, respectively. Table 1 Ê ) in a LiKSO4 crystal at room temperature The bond-lengths (A Bond
Ê) Bond-length (A
Bond
Ê) Bond-length (A
Li±O(1) Li±O(2) Li±O(3) Li±O(4)
1.930 2.010 1.890 1.890
K±O(1) K±O(2) K±O(3) K±O(4) K±O(5) K±O(6) K±O(7) K±O(8) K±O(9)
2.870 3.230 2.870 2.890 2.760 2.830 2.920 3.200 3.200
4. Experimental results and analysis The quadrupole perturbed NMR spectra have been analyzed using the usual spin Hamiltonian [22,23].
1 1} 12 3cos2 u 2 1 1
1 2
hsin2 ucos2w
1 second 2 order quadrupolar terms 1 ¼ where HZ is the Zeeman term and HQ describes the nuclear electric quadrupole interaction of the 7Li (natural abundance 92.58%) and 39K (natural abundance 93.1%) nuclei, both of which have spin I 3/2. The rotation pattern of Li measured in the crystallographic ab-plane at room temperature is shown in Fig. 2(a). The central transition is stronger than the satellite lines, and the separations between adjacent lines are almost equal. The frequency difference between the maximum and minimum separation was about 3300 Hz. Therefore, the electric ®eld gradient tensor of Li is non-axially symmetric. This pattern proves to be slightly different from that in an earlier report [19], which indicated axial symmetry. The rotation pattern in the ca-plane is shown in Fig. 2(b). The maximum separation resulting from the quadrupole interaction was observed when the magnetic ®eld was applied along the c-axis of the crystal. This direction was determined to be the Z-axis of the EFG tensor. The satellite resonance lines show the angular dependence of
A.R. Lim, S.-Y. Jeong / Journal of Physics and Chemistry of Solids 62 (2001) 881±885
883
Fig. 2. The rotation patterns of 7Li NMR in the ab-, and ca-planes.
3cos 2 u 2 1, where the polar angle u is the direction of the magnetic ®eld with respect to the c-axis. The quadrupole parameters were determined by the least-squares ®t using the experimental data of Fig. 2(a) and (b). From these NMR results, the quadrupole coupling constant, e 2qH/h 25 kHz, and the asymmetry parameter, h 0.15, of 7Li were determined at room temperature. The EFG tensor of 7Li was found to be non-axially symmetric, consistent with the crystal structure as previously reported [24]; the lithium ion is surrounded by oxygen atoms located at a slightly distorted tetrahedron as shown in Fig. 1. The rotation patterns of 39K were measured in the two crystallographic planes at room temperature as shown in Fig. 3(a) and (b). Dots correspond to the experimental values and the full curves were obtained by ®tting these data to symmetric second rank EFG tensors. These rotation
patterns indicate anisotropic EFG tensors. The 39K NMR spectrum consists of only one resonance line for all orientations of the crystal in the external magnetic ®eld. From this fact, it was concluded that all the potassium sites in the LiKSO4 crystal are magnetically equivalent at room temperature. The largest resonance frequency was observed when the magnetic ®eld was applied along the c-axis of the crystal. This direction was determined to be the Z-axis of the EFG tensor. Based on these NMR results, the quadrupole coupling constant, e 2qH/h 1.28 MHz, and the asymmetry parameter, h 0.18, of 39K were determined at room temperature. The EFG tensor of 39K was found to be nonaxially symmetric; the potassium ion is surrounded by oxygen atoms located at nine distorted tetrahedra. The parameters analyzed for the 7Li and 39K nuclei are summarized in Table 2 together with those from previous reports.
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A.R. Lim, S.-Y. Jeong / Journal of Physics and Chemistry of Solids 62 (2001) 881±885
Fig. 3. The rotation patterns of 39K NMR in the ab-, and ca-planes.
5. Discussion and conclusion A diagram of the symmetry elements and of the general position for C66 is shown in Fig. 4. The following positions (Wyckoff notation and point symmetry) are occupied; 2Li
(b, 3), 2K (a, 3), 2S (b, 3), and 6O (c, 1) [25]. The local symmetry at the Li and K site in LiKSO4 is symbol 3 symmetry. The stereographic projection for symbol 3 is shown in Fig. 4. The symbol 3 signi®es that the principal axis is a triad. Starting from the initial pole of a general face,
Table 2 Quadrupole parameters of the 7Li and 39K in LikKSO4 at room temperature Nucleus
e 2qQ/h
h
Principal axes
References
7
25 kHz 35.8 kHz 1.28 MHz 1.27 MHz
0.15 0 0.18 0
X a, Y b, Z c
Lim et al. [24] Meng and Cao [19] Present work Topic et al. [18]
Li
39
K
X a, Y b, Z c X a, Y b, Z c
A.R. Lim, S.-Y. Jeong / Journal of Physics and Chemistry of Solids 62 (2001) 881±885
885
References
Fig. 4. (a) The symmetry elementary for C66 and (b) the sterographic projection for the symbol 3.
we obtained three poles related to each other by the rotation axis. This means that the two sites are crystallographically and magnetically equivalent. Therefore, only one set of the NMR spectra of 7Li and 39K was obtained, even though there are two lithium and potassium nuclei per unit cell. From the 7Li and 39K NMR results, the quadrupole coupling constant, asymmetry parameter, and the direction of EFG tensor were determined at room temperature. The principal axes of the EFG tensor for the 7Li ion were the same as those for the 39K ion. The EFG tensor of 7Li and 39K was found to be non-axially symmetric. The NMR results with the asymmetry parameters are consistent with the crystal structure of a slightly distorted LiO4 tetrahedron as represented in Table 1; the lithium ion is surrounded by oxygen atoms located on a slightly distorted tetrahedron as shown in Fig. 1. The resultant coordinating potassium ion is surrounded by oxygen atoms located at nine distorted tetrahedra. These results are not consistent with previous results [18,19]. Therefore, the structure of LiKSO4 crystal seems to be dependent on the conditions of crystal growth. The information about the asymmetry parameter was determined by ions surrounding the resonant nucleus. Acknowledgements This work was supported by the Korean Physical Society (1999).
[1] T. Breczewski, T. Krajewski, B. Mroz, Ferroelectrics 33 (1981) 9. [2] R. Cach, P.E. Tomaszewski, P. Bastie, J. Bornarel, Ferroelectrics 53 (1984) 337. [3] R. Cach, P.E. Tomaszewski, J. Bornarel, J. Phys. C: Solid State Phys. 18 (1985) 915. [4] J.M. Filho, J.E. Moreira, F.E.A. Melo, F.A. Germano, A.S.B. Sombra, Solid State Commun. 60 (1986) 189. [5] F. Holuj, M. Drozdowski, Ferroelectrics 36 (1981) 379. [6] C.H.A. Fonseca, G.M. Ribeiro, R. Gazzinelli, A.S. Chaves, Solid State Commun. 46 (1983) 221. [7] J.T. Yu, J.M. Kou, S.J. Huang, L.S. Co, J. Phys. Chem. Solids 47 (1986) 121. [8] K. Murthy, S.V. Bhat, J. Phys. C: Solid State Phys. 21 (1988) 597. [9] N.R. Ivanov, Ferroelectrics 64 (1985) 13. [10] G. Sorge, H. Hempel, Phys. Stat. Sol.(a) 97 (1986) 431. [11] W. Kleemann, F.J. Schafer, A.S. Chaves, Solid State Commun. 64 (1987) 1001. [12] J. Ortega, J. Etxebarria, T.J. Breczewski, Appl. Cryst. 26 (1993) 549. [13] M.L. Bansal, S.K. Deb, A.P. Roy, V.C. Sahni, Solid State Commun. 36 (1980) 1047. [14] D. Teeters, R. Frech, Phys. Rev. B 26 (1982) 4132. [15] D. Teeters, R. Frech, Phys. Rev. B 26 (1982) 5897. [16] A.J. Oliveira, F.A. Germano, J.M. Filho, F.E.A. Melo, J.E. Moreira, Phys. Rev. B 38 (1988) 12633. [17] M. Karppinen, J.O. Lundgren, R. Liminga, Acta Cryst. C 39 (1983) 34. [18] B. Topic, U. Haeberlen, R. Blinc, Z. Phys. BÐCondensed Matter 70 (1988) 95. [19] Q.A. Meng, J. Cao, Acta Physica Sinica 31 (1982) 1045. [20] P.A. Sandomirskii, S.S. Meshalkin, I.V. Rozhdestvenskaya, Sov. Phys. Crystallogr. 28 (1983) 33. [21] M.A. Pimenta, P. Echegut, Y. Luspin, G. Hauret, F. Gervais, P. Abelard, Phys. Rev. B 39 (1989) 3361. [22] A. Abragam, The Principles of Nuclear Magnetism, Oxford University Press, Oxford, 1961. [23] C.P. Slichter, Principles of Magnetic Resonance, SpringerVerlag, New York, 1989. [24] A.R. Lim, S.H. Choh, S.Y. Jeong, J. Phys.: Condes. Matter 8 (1996) 4597. [25] T. Hahn, Space-Group Symmetry, International Tables for Crystallography A, The International Union of Crystallography, New York, 1987.
www.elsevier.nl/locate/jpcs
Tetrahedral structure in LiKSO4 crystals studied by 7Li and 39 K NMR Ae Ran Lim a,*, Se-Young Jeong b b
a Department of Physics, Jeonju University, Jeonju 560-759, South Korea Department of Physics, Pusan National University, Pusan 609-735, South Korea
Received 9 March 2000; accepted 20 June 2000
Abstract The 7Li and 39K nuclear magnetic resonances in a LiKSO4 single crystal grown by the slow evaporation method were investigated by employing an NMR spectrometer. From the experimental data, the quadrupole coupling constant and asymmetry parameter were determined at room temperature. The principal axes corresponding to the largest principal value of the 7 Li and 39K EFG tensors were parallel to the hexagonal c-axis. This direction was determined to be the Z-axis of the EFG tensor. The EFG tensor of 7Li and 39K was found to be non-axially symmetric; the lithium ion is surrounded by oxygen atoms located at a slightly distorted tetrahedron, and the resultant coordinating potassium ion was enclosed by the oxygen atoms located at nine distorted tetrahedra. q 2001 Elsevier Science Ltd. All rights reserved. Keywords: B. Crystal growth; D. Crystal structure; D. Nuclear magnetic resonance (NMR)
1. Introduction The search for LiKSO4 crystals having excellent optical quality has been extensive, and much has been reported about their physical properties. In spite of the many experiments, however, the nature of the structural phase transitions in LiKSO4 is still not well understood. LiKSO4 exhibits a rich variety of phase transitions in the temperature range 10 to 1000 K. The results of dielectric studies [1±4], EPR [5±8], optical properties [9±12], and Raman scattering measurements [13±16] for the phase transitions are not consistent. The structure of LiKSO4 at room temperature is hexagonal with space group P63 C66 and two formula units per cell [17]. It consists of alternating stacked SO4 and LiO4 tetrahedra with common oxygen tops. The K 1 ions lie on the hexagonal axis and are surrounded by nine oxygens. Topic et al. [18] have made a 39K NMR analysis of LiKSO4 at room temperature. According to their results, the rotation pattern in the ab-plane was angle independent, while the rotation patterns in the ac- and bc-planes were angle dependent. From these results, it was determined that the quadrupole * Corresponding author. Tel.: 182-63-220-2514; fax: 182-63220-2362. E-mail address: [email protected] (A.R. Lim).
coupling constant e 2qQ/h 1.27 MHz, asymmetry parameter h 0, and the principal axis corresponding to the largest principal value was parallel to the hexagonal c-axis. Also, the 7Li NMR results reported by Meng et al. [19] showed a quadrupole coupling constant e 2qQ/h 35.8 kHz and asymmetry parameter h 0. In both these studies, the electric ®eld gradient tensors of 7Li and 39K NMR were axially symmetric. However, the asymmetry parameter in LiKSO4 crystals studied by the two groups above was not consistent with the crystal structure of a slightly distorted LiO4 tetrahedron [20]. Our present work deals with the 7Li and 39K NMR in a LiKSO4 single crystal grown by the slow evaporation method. The quadrupole coupling constant, e 2qQ/h, and asymmetry parameter, h , of 7Li and 39K NMR in a LiKSO4 single crystal were analyzed through experimental data obtained with a pulse NMR spectrometer. We herein examine the crystal structure of LiKSO4 crystals through the NMR of 7Li and 39K nuclei.
2. Crystal structure LiKSO4 (lithium potassium sulfate) crystals are hexagonal with two molecular formula units per unit cell. The Ê lattice parameters of the hexagonal cell are a 5.147 A
0022-3697/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved. PII: S 0022-369 7(00)00244-4
882
A.R. Lim, S.-Y. Jeong / Journal of Physics and Chemistry of Solids 62 (2001) 881±885
Fig. 1. (a) The hexagonal structure and (b) the projection in the (0001) plane of a LiKSO4 single crystal at room temperature.
Ê at room temperature [21]. The hexagonal and c 8.633 A structure and the projection in the (0001) plane of LiKSO4 single crystals are shown in Fig. 1(a) and (b), respectively. The SO4 and LiO4 tetrahedra form an ordered, three dimensional framework structure characterized by six-membered rings of three LiO4 and three SO4 tetrahedra. The apices of the three LiO4 tetrahedra point in the opposite direction from those of the three SO4 tetrahedra. The K atoms occupy positions on the hexagonal c-axis. They are coordinated by nine oxygens. The bond lengths for Li±O and K±O are listed in Table 1 [20].
Nuclear magnetic resonance signals of 7Li and 39K NMR in a LiKSO4 single crystal were measured using Bruker MSL 200 MHz NMR and DSX 400 MHz NMR spectrometer at the Korea Basic Science Institute. The static magnetic ®eld was 4.7 and 9.4 T, and the central radio frequency was set at v 0/2p 77.777 MHz for the 7Li nucleus and v 0/2p 18.676 MHz for the 29K nucleus.
3. Experimental procedure
H HZ 1 HQ 2g"B0 ´I 1 e2 qQ=4I 2I 2 1{3Iz2 2 I I
Single crystals of LiKSO4 were grown by slow evaporation from an aqueous solution at 328C. The solution contained equimolar amounts of Li2SO4.H2O and K2SO4. The colorless single crystals prepared were about 5 £ 5 £ 10 mm 3. The orientations of the crystal were determined by the X-ray Laue method. The angular dependence of the NMR spectra was measured on the crystallographic ab-, bc-, and ca-planes, respectively. Table 1 Ê ) in a LiKSO4 crystal at room temperature The bond-lengths (A Bond
Ê) Bond-length (A
Bond
Ê) Bond-length (A
Li±O(1) Li±O(2) Li±O(3) Li±O(4)
1.930 2.010 1.890 1.890
K±O(1) K±O(2) K±O(3) K±O(4) K±O(5) K±O(6) K±O(7) K±O(8) K±O(9)
2.870 3.230 2.870 2.890 2.760 2.830 2.920 3.200 3.200
4. Experimental results and analysis The quadrupole perturbed NMR spectra have been analyzed using the usual spin Hamiltonian [22,23].
1 1} 12 3cos2 u 2 1 1
1 2
hsin2 ucos2w
1 second 2 order quadrupolar terms 1 ¼ where HZ is the Zeeman term and HQ describes the nuclear electric quadrupole interaction of the 7Li (natural abundance 92.58%) and 39K (natural abundance 93.1%) nuclei, both of which have spin I 3/2. The rotation pattern of Li measured in the crystallographic ab-plane at room temperature is shown in Fig. 2(a). The central transition is stronger than the satellite lines, and the separations between adjacent lines are almost equal. The frequency difference between the maximum and minimum separation was about 3300 Hz. Therefore, the electric ®eld gradient tensor of Li is non-axially symmetric. This pattern proves to be slightly different from that in an earlier report [19], which indicated axial symmetry. The rotation pattern in the ca-plane is shown in Fig. 2(b). The maximum separation resulting from the quadrupole interaction was observed when the magnetic ®eld was applied along the c-axis of the crystal. This direction was determined to be the Z-axis of the EFG tensor. The satellite resonance lines show the angular dependence of
A.R. Lim, S.-Y. Jeong / Journal of Physics and Chemistry of Solids 62 (2001) 881±885
883
Fig. 2. The rotation patterns of 7Li NMR in the ab-, and ca-planes.
3cos 2 u 2 1, where the polar angle u is the direction of the magnetic ®eld with respect to the c-axis. The quadrupole parameters were determined by the least-squares ®t using the experimental data of Fig. 2(a) and (b). From these NMR results, the quadrupole coupling constant, e 2qH/h 25 kHz, and the asymmetry parameter, h 0.15, of 7Li were determined at room temperature. The EFG tensor of 7Li was found to be non-axially symmetric, consistent with the crystal structure as previously reported [24]; the lithium ion is surrounded by oxygen atoms located at a slightly distorted tetrahedron as shown in Fig. 1. The rotation patterns of 39K were measured in the two crystallographic planes at room temperature as shown in Fig. 3(a) and (b). Dots correspond to the experimental values and the full curves were obtained by ®tting these data to symmetric second rank EFG tensors. These rotation
patterns indicate anisotropic EFG tensors. The 39K NMR spectrum consists of only one resonance line for all orientations of the crystal in the external magnetic ®eld. From this fact, it was concluded that all the potassium sites in the LiKSO4 crystal are magnetically equivalent at room temperature. The largest resonance frequency was observed when the magnetic ®eld was applied along the c-axis of the crystal. This direction was determined to be the Z-axis of the EFG tensor. Based on these NMR results, the quadrupole coupling constant, e 2qH/h 1.28 MHz, and the asymmetry parameter, h 0.18, of 39K were determined at room temperature. The EFG tensor of 39K was found to be nonaxially symmetric; the potassium ion is surrounded by oxygen atoms located at nine distorted tetrahedra. The parameters analyzed for the 7Li and 39K nuclei are summarized in Table 2 together with those from previous reports.
884
A.R. Lim, S.-Y. Jeong / Journal of Physics and Chemistry of Solids 62 (2001) 881±885
Fig. 3. The rotation patterns of 39K NMR in the ab-, and ca-planes.
5. Discussion and conclusion A diagram of the symmetry elements and of the general position for C66 is shown in Fig. 4. The following positions (Wyckoff notation and point symmetry) are occupied; 2Li
(b, 3), 2K (a, 3), 2S (b, 3), and 6O (c, 1) [25]. The local symmetry at the Li and K site in LiKSO4 is symbol 3 symmetry. The stereographic projection for symbol 3 is shown in Fig. 4. The symbol 3 signi®es that the principal axis is a triad. Starting from the initial pole of a general face,
Table 2 Quadrupole parameters of the 7Li and 39K in LikKSO4 at room temperature Nucleus
e 2qQ/h
h
Principal axes
References
7
25 kHz 35.8 kHz 1.28 MHz 1.27 MHz
0.15 0 0.18 0
X a, Y b, Z c
Lim et al. [24] Meng and Cao [19] Present work Topic et al. [18]
Li
39
K
X a, Y b, Z c X a, Y b, Z c
A.R. Lim, S.-Y. Jeong / Journal of Physics and Chemistry of Solids 62 (2001) 881±885
885
References
Fig. 4. (a) The symmetry elementary for C66 and (b) the sterographic projection for the symbol 3.
we obtained three poles related to each other by the rotation axis. This means that the two sites are crystallographically and magnetically equivalent. Therefore, only one set of the NMR spectra of 7Li and 39K was obtained, even though there are two lithium and potassium nuclei per unit cell. From the 7Li and 39K NMR results, the quadrupole coupling constant, asymmetry parameter, and the direction of EFG tensor were determined at room temperature. The principal axes of the EFG tensor for the 7Li ion were the same as those for the 39K ion. The EFG tensor of 7Li and 39K was found to be non-axially symmetric. The NMR results with the asymmetry parameters are consistent with the crystal structure of a slightly distorted LiO4 tetrahedron as represented in Table 1; the lithium ion is surrounded by oxygen atoms located on a slightly distorted tetrahedron as shown in Fig. 1. The resultant coordinating potassium ion is surrounded by oxygen atoms located at nine distorted tetrahedra. These results are not consistent with previous results [18,19]. Therefore, the structure of LiKSO4 crystal seems to be dependent on the conditions of crystal growth. The information about the asymmetry parameter was determined by ions surrounding the resonant nucleus. Acknowledgements This work was supported by the Korean Physical Society (1999).
[1] T. Breczewski, T. Krajewski, B. Mroz, Ferroelectrics 33 (1981) 9. [2] R. Cach, P.E. Tomaszewski, P. Bastie, J. Bornarel, Ferroelectrics 53 (1984) 337. [3] R. Cach, P.E. Tomaszewski, J. Bornarel, J. Phys. C: Solid State Phys. 18 (1985) 915. [4] J.M. Filho, J.E. Moreira, F.E.A. Melo, F.A. Germano, A.S.B. Sombra, Solid State Commun. 60 (1986) 189. [5] F. Holuj, M. Drozdowski, Ferroelectrics 36 (1981) 379. [6] C.H.A. Fonseca, G.M. Ribeiro, R. Gazzinelli, A.S. Chaves, Solid State Commun. 46 (1983) 221. [7] J.T. Yu, J.M. Kou, S.J. Huang, L.S. Co, J. Phys. Chem. Solids 47 (1986) 121. [8] K. Murthy, S.V. Bhat, J. Phys. C: Solid State Phys. 21 (1988) 597. [9] N.R. Ivanov, Ferroelectrics 64 (1985) 13. [10] G. Sorge, H. Hempel, Phys. Stat. Sol.(a) 97 (1986) 431. [11] W. Kleemann, F.J. Schafer, A.S. Chaves, Solid State Commun. 64 (1987) 1001. [12] J. Ortega, J. Etxebarria, T.J. Breczewski, Appl. Cryst. 26 (1993) 549. [13] M.L. Bansal, S.K. Deb, A.P. Roy, V.C. Sahni, Solid State Commun. 36 (1980) 1047. [14] D. Teeters, R. Frech, Phys. Rev. B 26 (1982) 4132. [15] D. Teeters, R. Frech, Phys. Rev. B 26 (1982) 5897. [16] A.J. Oliveira, F.A. Germano, J.M. Filho, F.E.A. Melo, J.E. Moreira, Phys. Rev. B 38 (1988) 12633. [17] M. Karppinen, J.O. Lundgren, R. Liminga, Acta Cryst. C 39 (1983) 34. [18] B. Topic, U. Haeberlen, R. Blinc, Z. Phys. BÐCondensed Matter 70 (1988) 95. [19] Q.A. Meng, J. Cao, Acta Physica Sinica 31 (1982) 1045. [20] P.A. Sandomirskii, S.S. Meshalkin, I.V. Rozhdestvenskaya, Sov. Phys. Crystallogr. 28 (1983) 33. [21] M.A. Pimenta, P. Echegut, Y. Luspin, G. Hauret, F. Gervais, P. Abelard, Phys. Rev. B 39 (1989) 3361. [22] A. Abragam, The Principles of Nuclear Magnetism, Oxford University Press, Oxford, 1961. [23] C.P. Slichter, Principles of Magnetic Resonance, SpringerVerlag, New York, 1989. [24] A.R. Lim, S.H. Choh, S.Y. Jeong, J. Phys.: Condes. Matter 8 (1996) 4597. [25] T. Hahn, Space-Group Symmetry, International Tables for Crystallography A, The International Union of Crystallography, New York, 1987.