- Email: [email protected]
Low energy vibrational excitations characteristic of superionic glass
ARTICLE IN PRESS
Physica B 385–386 (2006) 552–554 www.elsevier.com/locate/physb
Low energy vibrational excitations characteristic of superionic glass M. Nakamuraa,, H. Iwaseb, M. Araia, E. Kartinic, M. Russinad, T. Yokooe, J.W. Taylorf a
Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan c Industrial Material Division, R & D Center for Materials Science and Technology, BATAN, Serpong, Tangerang 15314, Indonesia d Hahn-Meitner-Institut, Glienicker Strasse 100, 14109 Berlin, Germany e Institute of Materials Structure Science, KEK, 1-1 Oho, Tsukuba 305-0801, Japan f Rutherford Appleton Laboratory, ISIS, Chilton Didcot, Oxon OX11, UK b
Abstract The mechanism of high ionic conductivity in superionic glass constitutes an unsolved problem in the field of science. Here we performed inelastic neutron scattering measurements of superionic glass system ðAgIÞx ðAg2 SÞx ðAgPO3 Þ12x by using MARI spectrometer at ISIS, and found that the Q-dependence of inelastic intensity in the energy region from 1 to 3 meV of superionic phase glass shows an excess intensity above Q ¼ 1:8 A˚ 1 compared with insulator phase. Similar phenomena were also observed in another superionic glass ðAgIÞ0:5 ðAgPO3 Þ0:5 by using NEAT spectrometer at HMI with high resolution measurement. These results clearly suggest peculiar low energy vibrational excitations should be universal features of superionic glass. r 2006 Elsevier B.V. All rights reserved. PACS: 61.43.Fs; 66.10.Ed; 78.70.Nx Keywords: Superionic glass; Ionic conductivity; Low-energy dynamics
1. Introduction Superionic glasses play a prominent role in many solid electrolyte applications including batteries, sensors, and displays [1]. However, the mechanism of high ionic conductivity in disordered structures constitute an unsolved problem in the field of science. Particular efforts have been directed to the AgI-doped silver oxysalt glasses such as ðAgIÞx ðAgPO3 Þ1x system, because they have high room-temperature ionic conductivity and are easy to produce. The ionic conductivity at room temperature of ðAgIÞx ðAgPO3 Þ1x glasses varies in the range of 107 S=cm (x ¼ 0:00) to 102 S=cm (x ¼ 0:50) [2]. In addition, the superionic glasses of ðAg2 SÞx ðAgPO3 Þ1x system are also well studied by several experimental methods. However, it is well known that the role of AgI in high ionic conductivity of AgPO3 -based glass is evidently different from that of Ag2 S. The AgPO3 glassy matrix is unaffected by AgICorresponding author: Tel.: 81 29282 6936; fax: 81 29284 3889.
E-mail address: [email protected] (M. Nakamura). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.05.274
doping, while Ag2 S has a tendency to cut the chains of AgPO3 tetrahedra, which means that it is possible to control chain length by adding Ag2 S as a glass modifier [3]. A study of the ternary AgI2Ag2 S2AgPO3 glass system [4] should be important for complete understanding of the essential mechanism of high ionic conductivity in silver oxysalt–silver salt glasses. The ðAgIÞx ðAg2 SÞx ðAgPO3 Þ12x glass systems have been widely investigated in terms of structure, conductivity, and thermal properties [4,5]. The ionic conductivity of ðAgIÞx ðAg2 SÞx ðAgPO3 Þ12x with x ¼ 0:33 reaches a value of 102 S=cm. So far there have been few studies to relate the high ionic conductivity of superionic glasses to their vibrational properties. In this paper, we will represent the low-energy vibrational excitations characteristic of superionic glasses by inelastic neutron scattering measurement. 2. Experimental procedures The silver oxysalt glasses AgPO3 , ðAgIÞ0:5 ðAgPO3 Þ0:5 , and ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPO3 Þ0:34 were prepared by a
ARTICLE IN PRESS M. Nakamura et al. / Physica B 385–386 (2006) 552–554
(a) 300
x=0.33
Intensity (a. u.)
(AgI)x(Ag2S)x(AgPO3)1-2x
x=0.00
200
100
MARI -1 meV < E< 1 meV
0 25
(b) 20 MARI Intensity (a. u.)
standard melt quenching method and the procedures were described elsewhere [6]. The inelastic neutron scattering measurements both for AgPO3 and ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPOÞ0:34 glasses were performed on the MARI spectrometer at the ISIS spallation neutron source in the Rutherford Appleton Laboratory, UK. A selected incident energy was 15 meV with an energy resolution of 0.5 meV. In addition, we also carried out the inelastic neutron scattering measurements for ðAgIÞ0:5 ðAgPO3 Þ0:5 glass besides AgPO3 and ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPO3 Þ0:34 glasses by using the NEAT spectrometer at the Berlin Neutron Scattering Center in the HanhMeitner Institute, Germany. A selected elastic energy resolution was 187 meV by a incident wavelength of 4 A˚. The 141 detectors were grouped into 17 groups in order to improve the statistics of data. All of the measurements in MARI and NEAT were performed at room temperature, and normalization was made by a vanadium standard.
553
15 10
3. Results and discussion
5
We have observed the low-energy excitations of ðAgIÞx ðAg2 SÞx ðAgPO3 Þ12x glasses with x ¼ 0 (insulator phase) and 0.33 (superionic phase) by using the MARI spectrometer. The result is shown in Fig. 1, where the lowenergy intensity (below 5 meV) of the x ¼ 0:33 sample is much larger than that of the x ¼ 0 sample. It is clear that the superionic phase glass has an excess of the vibrational density of states (VDOS), compared with insulator phase glass. Fig. 2(a) shows the elastic structure factor S el ðQÞ of ðAgIÞx ðAg2 SÞx ðAgPO3 Þ12x glasses with x ¼ 0 and 0.33,
0
1 meV < E < 3meV
10 MARI
Intensity (a. u.)
8
6
4 (AgI)x(Ag2S)x(AgPO3)1-2x 2
x=0.33 x=0.0
0 0
2
4 6 Energy (meV)
8
10
Fig. 1. The E dependence of SðQ; EÞ integrated over Q for ðAgIÞx ðAg2 SÞx ðAgPO3 Þ12x glasses with x ¼ 0 and 0.33. Measurements were performed on the MARI spectrometer. Both data were taken at room temperature and corrected by Bose factor.
0
1
2
3
4
5
Q (A-1)
Fig. 2. Q dependences of the SðQ; EÞ are plotted for ðAgIÞx ðAg2 SÞx ðAgPO3 Þ12x glasses with x ¼ 0 and 0.33; (a) elastic component integrated between 1 and 1 meV, and (b) inelastic component integrated between 1 and 3 meV.
obtained from an integration between 1 and 1 meV of dynamical structure factor SðQ; EÞ. A clear peak at an anomalously low Q region ð0:60:8 A˚ 1 Þ, appears only in superionic phase glass with x ¼ 0:33 [5]. In this paper, we refer to this peak as a ‘‘prepeak’’. The appearance of a prepeak in neutron diffraction measurement was also reported for ðAgIÞx ðAgPO3 Þ1x glasses [7]. The Q dependences of low-energy region between 1 and 3 meV for both samples are compared in Fig. 2(b), which clearly indicate that an excess intensity of the x ¼ 0:33 sample is caused by unique dynamics in the Q range beyond 1:8 A˚ 1 . We can also observe the peak profile at around Q ¼ 2:2 A˚ 1 only in the x ¼ 0:33 sample. It should be noted that Q 2:2 A˚ 1 corresponds to the peak observed in elastic structure factors S el ðQÞ for both x ¼ 0 and x ¼ 0:33 samples in Fig. 2(a). On the other hand, we can find no inelastic contributions at a prepeak position both for insulator and superionic phase glasses. These results suggest the cooperative vibrations in the low-energy region occur only in superionic phase glass, and should provide clues to understanding the high ionic conductivity of superionic glasses. Hence, it becomes important to confirm the universality of these phenomena. We have investigated the Q dependent feature in the low-energy region for ðAgIÞ0:5 ðAgPO3 Þ0:5 glass. The ðAgIÞ0:5 ðAgPO3 Þ0:5 glass is a typical superionic glass and
ARTICLE IN PRESS M. Nakamura et al. / Physica B 385–386 (2006) 552–554
554
4. Conclusion
0.030
In this study, we have performed the inelastic neutron scattering measurements of superionic glasses; ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPO3 Þ0:34 and ðAgIÞ0:5 ðAgPO3 Þ0:5 . In order to make a comparison between superionic glass and insulator one, we have also measured an inelastic neutron scattering of AgPO3 glass. The superionic phase glasses have shown the peculiar dynamics in low-energy region beyond Q ¼ 1:8 A˚ 1 , which causes an excess VDOS in low-energy region for superionic phase glasses, compared with insulator phase glass. We have pointed out capability to realize the coherent atomic correlations should be inherent in superionic glasses.
(AgI)x(Ag2S)x(AgPO3)1-2x ; x=0.33 0.025
(AgI)x(AgPO3)1-x ; x=0.50 AgPO3
Intensity (a. u.)
0.020
NEAT
0.015
0.010
0.005
Acknowledgments
0.000 0.0
0.5
1.0
1.5 Q (A-1)
2.0
2.5
3.0
Fig. 3. Same as in Fig. 2(b), but the Q dependence of SðQ; EÞ averaged over from 1 to 3 meV is plotted for ðAgIÞ0:5 ðAgPO3 Þ0:5 glass besides AgPO3 and ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPO3 Þ0:34 glasses. Measurements were performed on the NEAT spectrometer at room temperature.
shows high ionic conductivity at room temperature ðs102 S=cm1 Þ. Fig. 3 shows the Q dependences of SðQ; EÞ in the low-energy region for three types of glasses, that is AgPO3 , ðAgIÞ0:5 ðAgPO3 Þ0:5 , and ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPO3 Þ0:34 , where each intensity was averaged over from 1 to 3 meV. The neutron scattering data in Fig. 3 were collected by using NEAT spectrometer at room temperature. We confirmed that ðAgIÞ0:5 ðAgPO3 Þ0:5 glass also gives an excess intensity in the low-energy region, compared with AgPO3 glass [8]. It is obvious that unique dynamics in the Q range beyond 1:8 A˚ 1 also appears in ðAgIÞ0:5 ðAgPO3 Þ0:5 glass. This behavior is almost the same as that of ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPO3 Þ0:34 sample. A peak at around Q 2:2 A˚ 1 may be related to a distance d in real space by the expression 2p=Q ¼ d. For ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPO3 Þ0:34 and ðAgIÞ0:5 ðAgPO3 Þ0:5 ˚ which can be assigned to the glasses this gives d 2:8 A, Ag–Ag correlation [9]. It seems reasonable to conclude that the silver oxysalt superionic glasses intrinsically realize the coherent atomic correlations.
The neutron scattering experiment in ISIS facility was performed under the Japan-UK Collaboration Programme on Neutron Scattering. This work was supported by a Grant-in-Aid for Creative Scientific Research (No. 16GS0417) and Specially Promoted Research (No. 17001001) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
References [1] M. Balkanski, Phys. World 3 (1990) 29. [2] J.P. Malugani, A. Wasniewski, M. Doreau, G. Robert, A. Al Rikabi, Mat. Res. Bull. 13 (1978) 427. [3] M.F. Collins, E. Kartini, Recent Rep. Devel. Solid State Ionics 1 (2003) 157. [4] J.M. Reau, Liu Jun, B. Tanguy, J.J. Videau, J. Portier, P. Hagenmuller, J. Solid State Chem. 85 (1990) 228. [5] E. Kartini, S.J. Kennedy, T. Sakuma, K. Itoh, T. Fukunaga, M.F. Collins, T. Kamiyama, S. Suminta, A. Suguharto, E. Musyafaah, P. Bawano, J. Non-Cryst. Solids 312–314 (2002) 628. [6] E. Kartini, M.F. Collins, T. Priyanto, M. Yusuf, N. Indayaningsih, E.C. Svensson, S.J. Kennedy, Phys. Rev. B 61 (2000) 1036. [7] L. Bo¨rjesson, L.M. Torell, U. Dahlborg, W.S. Howells, Phys. Rev. B 39 (1989) 3404. [8] H. Takahashi, Y. Hiki, T. Sakuma, S. Funahashi, Solid State Ionics 53–56 (1992) 1164. [9] J.D. Wicks, L. Bo¨rjesson, G. Bushnell-Wye, W.S. Howells, R.L. McGreevy, Phys. Rev. Lett. 74 (1995) 726.
Physica B 385–386 (2006) 552–554 www.elsevier.com/locate/physb
Low energy vibrational excitations characteristic of superionic glass M. Nakamuraa,, H. Iwaseb, M. Araia, E. Kartinic, M. Russinad, T. Yokooe, J.W. Taylorf a
Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan c Industrial Material Division, R & D Center for Materials Science and Technology, BATAN, Serpong, Tangerang 15314, Indonesia d Hahn-Meitner-Institut, Glienicker Strasse 100, 14109 Berlin, Germany e Institute of Materials Structure Science, KEK, 1-1 Oho, Tsukuba 305-0801, Japan f Rutherford Appleton Laboratory, ISIS, Chilton Didcot, Oxon OX11, UK b
Abstract The mechanism of high ionic conductivity in superionic glass constitutes an unsolved problem in the field of science. Here we performed inelastic neutron scattering measurements of superionic glass system ðAgIÞx ðAg2 SÞx ðAgPO3 Þ12x by using MARI spectrometer at ISIS, and found that the Q-dependence of inelastic intensity in the energy region from 1 to 3 meV of superionic phase glass shows an excess intensity above Q ¼ 1:8 A˚ 1 compared with insulator phase. Similar phenomena were also observed in another superionic glass ðAgIÞ0:5 ðAgPO3 Þ0:5 by using NEAT spectrometer at HMI with high resolution measurement. These results clearly suggest peculiar low energy vibrational excitations should be universal features of superionic glass. r 2006 Elsevier B.V. All rights reserved. PACS: 61.43.Fs; 66.10.Ed; 78.70.Nx Keywords: Superionic glass; Ionic conductivity; Low-energy dynamics
1. Introduction Superionic glasses play a prominent role in many solid electrolyte applications including batteries, sensors, and displays [1]. However, the mechanism of high ionic conductivity in disordered structures constitute an unsolved problem in the field of science. Particular efforts have been directed to the AgI-doped silver oxysalt glasses such as ðAgIÞx ðAgPO3 Þ1x system, because they have high room-temperature ionic conductivity and are easy to produce. The ionic conductivity at room temperature of ðAgIÞx ðAgPO3 Þ1x glasses varies in the range of 107 S=cm (x ¼ 0:00) to 102 S=cm (x ¼ 0:50) [2]. In addition, the superionic glasses of ðAg2 SÞx ðAgPO3 Þ1x system are also well studied by several experimental methods. However, it is well known that the role of AgI in high ionic conductivity of AgPO3 -based glass is evidently different from that of Ag2 S. The AgPO3 glassy matrix is unaffected by AgICorresponding author: Tel.: 81 29282 6936; fax: 81 29284 3889.
E-mail address: [email protected] (M. Nakamura). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.05.274
doping, while Ag2 S has a tendency to cut the chains of AgPO3 tetrahedra, which means that it is possible to control chain length by adding Ag2 S as a glass modifier [3]. A study of the ternary AgI2Ag2 S2AgPO3 glass system [4] should be important for complete understanding of the essential mechanism of high ionic conductivity in silver oxysalt–silver salt glasses. The ðAgIÞx ðAg2 SÞx ðAgPO3 Þ12x glass systems have been widely investigated in terms of structure, conductivity, and thermal properties [4,5]. The ionic conductivity of ðAgIÞx ðAg2 SÞx ðAgPO3 Þ12x with x ¼ 0:33 reaches a value of 102 S=cm. So far there have been few studies to relate the high ionic conductivity of superionic glasses to their vibrational properties. In this paper, we will represent the low-energy vibrational excitations characteristic of superionic glasses by inelastic neutron scattering measurement. 2. Experimental procedures The silver oxysalt glasses AgPO3 , ðAgIÞ0:5 ðAgPO3 Þ0:5 , and ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPO3 Þ0:34 were prepared by a
ARTICLE IN PRESS M. Nakamura et al. / Physica B 385–386 (2006) 552–554
(a) 300
x=0.33
Intensity (a. u.)
(AgI)x(Ag2S)x(AgPO3)1-2x
x=0.00
200
100
MARI -1 meV < E< 1 meV
0 25
(b) 20 MARI Intensity (a. u.)
standard melt quenching method and the procedures were described elsewhere [6]. The inelastic neutron scattering measurements both for AgPO3 and ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPOÞ0:34 glasses were performed on the MARI spectrometer at the ISIS spallation neutron source in the Rutherford Appleton Laboratory, UK. A selected incident energy was 15 meV with an energy resolution of 0.5 meV. In addition, we also carried out the inelastic neutron scattering measurements for ðAgIÞ0:5 ðAgPO3 Þ0:5 glass besides AgPO3 and ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPO3 Þ0:34 glasses by using the NEAT spectrometer at the Berlin Neutron Scattering Center in the HanhMeitner Institute, Germany. A selected elastic energy resolution was 187 meV by a incident wavelength of 4 A˚. The 141 detectors were grouped into 17 groups in order to improve the statistics of data. All of the measurements in MARI and NEAT were performed at room temperature, and normalization was made by a vanadium standard.
553
15 10
3. Results and discussion
5
We have observed the low-energy excitations of ðAgIÞx ðAg2 SÞx ðAgPO3 Þ12x glasses with x ¼ 0 (insulator phase) and 0.33 (superionic phase) by using the MARI spectrometer. The result is shown in Fig. 1, where the lowenergy intensity (below 5 meV) of the x ¼ 0:33 sample is much larger than that of the x ¼ 0 sample. It is clear that the superionic phase glass has an excess of the vibrational density of states (VDOS), compared with insulator phase glass. Fig. 2(a) shows the elastic structure factor S el ðQÞ of ðAgIÞx ðAg2 SÞx ðAgPO3 Þ12x glasses with x ¼ 0 and 0.33,
0
1 meV < E < 3meV
10 MARI
Intensity (a. u.)
8
6
4 (AgI)x(Ag2S)x(AgPO3)1-2x 2
x=0.33 x=0.0
0 0
2
4 6 Energy (meV)
8
10
Fig. 1. The E dependence of SðQ; EÞ integrated over Q for ðAgIÞx ðAg2 SÞx ðAgPO3 Þ12x glasses with x ¼ 0 and 0.33. Measurements were performed on the MARI spectrometer. Both data were taken at room temperature and corrected by Bose factor.
0
1
2
3
4
5
Q (A-1)
Fig. 2. Q dependences of the SðQ; EÞ are plotted for ðAgIÞx ðAg2 SÞx ðAgPO3 Þ12x glasses with x ¼ 0 and 0.33; (a) elastic component integrated between 1 and 1 meV, and (b) inelastic component integrated between 1 and 3 meV.
obtained from an integration between 1 and 1 meV of dynamical structure factor SðQ; EÞ. A clear peak at an anomalously low Q region ð0:60:8 A˚ 1 Þ, appears only in superionic phase glass with x ¼ 0:33 [5]. In this paper, we refer to this peak as a ‘‘prepeak’’. The appearance of a prepeak in neutron diffraction measurement was also reported for ðAgIÞx ðAgPO3 Þ1x glasses [7]. The Q dependences of low-energy region between 1 and 3 meV for both samples are compared in Fig. 2(b), which clearly indicate that an excess intensity of the x ¼ 0:33 sample is caused by unique dynamics in the Q range beyond 1:8 A˚ 1 . We can also observe the peak profile at around Q ¼ 2:2 A˚ 1 only in the x ¼ 0:33 sample. It should be noted that Q 2:2 A˚ 1 corresponds to the peak observed in elastic structure factors S el ðQÞ for both x ¼ 0 and x ¼ 0:33 samples in Fig. 2(a). On the other hand, we can find no inelastic contributions at a prepeak position both for insulator and superionic phase glasses. These results suggest the cooperative vibrations in the low-energy region occur only in superionic phase glass, and should provide clues to understanding the high ionic conductivity of superionic glasses. Hence, it becomes important to confirm the universality of these phenomena. We have investigated the Q dependent feature in the low-energy region for ðAgIÞ0:5 ðAgPO3 Þ0:5 glass. The ðAgIÞ0:5 ðAgPO3 Þ0:5 glass is a typical superionic glass and
ARTICLE IN PRESS M. Nakamura et al. / Physica B 385–386 (2006) 552–554
554
4. Conclusion
0.030
In this study, we have performed the inelastic neutron scattering measurements of superionic glasses; ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPO3 Þ0:34 and ðAgIÞ0:5 ðAgPO3 Þ0:5 . In order to make a comparison between superionic glass and insulator one, we have also measured an inelastic neutron scattering of AgPO3 glass. The superionic phase glasses have shown the peculiar dynamics in low-energy region beyond Q ¼ 1:8 A˚ 1 , which causes an excess VDOS in low-energy region for superionic phase glasses, compared with insulator phase glass. We have pointed out capability to realize the coherent atomic correlations should be inherent in superionic glasses.
(AgI)x(Ag2S)x(AgPO3)1-2x ; x=0.33 0.025
(AgI)x(AgPO3)1-x ; x=0.50 AgPO3
Intensity (a. u.)
0.020
NEAT
0.015
0.010
0.005
Acknowledgments
0.000 0.0
0.5
1.0
1.5 Q (A-1)
2.0
2.5
3.0
Fig. 3. Same as in Fig. 2(b), but the Q dependence of SðQ; EÞ averaged over from 1 to 3 meV is plotted for ðAgIÞ0:5 ðAgPO3 Þ0:5 glass besides AgPO3 and ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPO3 Þ0:34 glasses. Measurements were performed on the NEAT spectrometer at room temperature.
shows high ionic conductivity at room temperature ðs102 S=cm1 Þ. Fig. 3 shows the Q dependences of SðQ; EÞ in the low-energy region for three types of glasses, that is AgPO3 , ðAgIÞ0:5 ðAgPO3 Þ0:5 , and ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPO3 Þ0:34 , where each intensity was averaged over from 1 to 3 meV. The neutron scattering data in Fig. 3 were collected by using NEAT spectrometer at room temperature. We confirmed that ðAgIÞ0:5 ðAgPO3 Þ0:5 glass also gives an excess intensity in the low-energy region, compared with AgPO3 glass [8]. It is obvious that unique dynamics in the Q range beyond 1:8 A˚ 1 also appears in ðAgIÞ0:5 ðAgPO3 Þ0:5 glass. This behavior is almost the same as that of ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPO3 Þ0:34 sample. A peak at around Q 2:2 A˚ 1 may be related to a distance d in real space by the expression 2p=Q ¼ d. For ðAgIÞ0:33 ðAg2 SÞ0:33 ðAgPO3 Þ0:34 and ðAgIÞ0:5 ðAgPO3 Þ0:5 ˚ which can be assigned to the glasses this gives d 2:8 A, Ag–Ag correlation [9]. It seems reasonable to conclude that the silver oxysalt superionic glasses intrinsically realize the coherent atomic correlations.
The neutron scattering experiment in ISIS facility was performed under the Japan-UK Collaboration Programme on Neutron Scattering. This work was supported by a Grant-in-Aid for Creative Scientific Research (No. 16GS0417) and Specially Promoted Research (No. 17001001) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
References [1] M. Balkanski, Phys. World 3 (1990) 29. [2] J.P. Malugani, A. Wasniewski, M. Doreau, G. Robert, A. Al Rikabi, Mat. Res. Bull. 13 (1978) 427. [3] M.F. Collins, E. Kartini, Recent Rep. Devel. Solid State Ionics 1 (2003) 157. [4] J.M. Reau, Liu Jun, B. Tanguy, J.J. Videau, J. Portier, P. Hagenmuller, J. Solid State Chem. 85 (1990) 228. [5] E. Kartini, S.J. Kennedy, T. Sakuma, K. Itoh, T. Fukunaga, M.F. Collins, T. Kamiyama, S. Suminta, A. Suguharto, E. Musyafaah, P. Bawano, J. Non-Cryst. Solids 312–314 (2002) 628. [6] E. Kartini, M.F. Collins, T. Priyanto, M. Yusuf, N. Indayaningsih, E.C. Svensson, S.J. Kennedy, Phys. Rev. B 61 (2000) 1036. [7] L. Bo¨rjesson, L.M. Torell, U. Dahlborg, W.S. Howells, Phys. Rev. B 39 (1989) 3404. [8] H. Takahashi, Y. Hiki, T. Sakuma, S. Funahashi, Solid State Ionics 53–56 (1992) 1164. [9] J.D. Wicks, L. Bo¨rjesson, G. Bushnell-Wye, W.S. Howells, R.L. McGreevy, Phys. Rev. Lett. 74 (1995) 726.