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Phonon density of states in YBa2Cu3Ox
Physica C 162-164 (1989) 466-467 North-Holland
PHONON DENSITY OF STATES IN YBa2Cu3Ox V.G. BAR'YAKHTAR*, A.A. VASIL'KEVICH**, P.G. IVANITSKY**, V.T. KROTENKO**, A.N. MAISTRENKO**, A.E. MOROZOVSKY*, V.M. PAN*, M.V. PASECHNIK*, V.I. SLISENKO** *Institute of Metal Physic, Kiev, Ukr.SSR **Institute of Nuclear Physics, Kiev, Ukr.SSR Using the method of inelastic neutron scattering the lattice dynamics of YBa2Cu3Ox ceramics (x--6.95 and 6_3) was studied at 80 K and 290 IC The analysis of G(E) dependence revealed that with the decrease of temperature from 290 K to 80 K the noticeable changes in YBa2Cu3Ox spectrum take place, especially in the energy range above 40 meV. The reduction of oxygen concentration leads to dramatic changes in G(E) behaviour in the energy range 40-90 meV.
After establishing the superconductivity in
difference is observed at energies E=11.2, 13.7, 22.5
Y-Ba-Cu-O system 1 it was found that YBa2Cu3Ox
meV within the 36-51 MeV energy range and near 70
(x=6.95, Te=90 K) superconducting phase is an
meV.
orthorombie oxygen-deficient perovskite (sp.gr.Pmmm) 2. With the decrease of oxygen content in this system temperature of the transition into superconducting state becomes lower and when x < 6.4 the sample looses superconducting properties. Further decrease of oxygen the concentration up to x=6.2 leads
TABLE. I NEUTRON SCATTERING present work,6,7,8
16.3
one (sp.gr.P4/mmm) of order-disorder type in oxygen
18.1
sub-system at T=300 K 3"5.
17.7
7.9 14.0 14.3
18.0
18.2 19.2
20.0 22.5
23.1 23.7 124.4
conducted on time-of- flight spectrometer 9. For
25.6 25.0
obtaining the generalized density of phonon states G(E)
29.2
(in one phonon approximation) the angels of 103.3,
34.2
86.1, 70.9 were used for slow neutron scattering measurements. The average time of one spectrum
OPTICAL DATA II,12,13,1~
5.4 8.1 II.2i11.8 I0.8 12.0 13.7 15.0 14.2
to the phase transitions from orthorombie to tetragonal
Slow neutron scattering experiments were
MODEL i0
2~.2
i26.1
28.5
!27.3
25.6 27.5
36.0
31.2131.3 33.0 36.5 36.9
33.7
37 .t~ ~.9
50.0
52.7
The generalized phonon density of states G(E) for 54.6 55.5
G(E) measured at different temperature (300 K and 80 K) is observed. In case ofx=6.95 a significant
53.5 56.5
55.0
58.8
59.7
figure. One can see that with the decrease of oxygen concentration up to x=6.3 a slight difference between
39.2 41.5
~6.1 50.0
~5. o 48.0
YBa2Cu3Ox (x=6.95 and x=6.3) at T = 8 0 K (dotted line) and at 300 K (solid line) is represented in the
35.0
38.7
43.5 43.8
measurement was about 130 hours.
27.3 28.6
62.0
61.~i
70.0169.9
72.5
72.5
74./*
79.6
65.9
67.2 73.0
difference in G(E) spectra obtained for normal (T=300 K) and superconducting (T=80 K) state is seen. This
0921-4534/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland)
TABLE 1 Energies of the peaks in G(E), in meV.
76.6
V.G. Bar'yakhtar et al. / Phonon density of states YBa2Cu30~
467
content, a slight spectrum transformation at the energies less than 30 meV (except the peaks at 11.2 and 13.7 meV) and a considerable spectrum transformation i t
2o
I
at above 30 meV take place. This confirms, on one
t
/ /' ~ I
'',
hand, the essential contribution of oxygen in the high-frequency range, and on the other hand, the changes in low-frequency part imply corresponding changes of practically all strength constants resulting from the decrease in oxygen concentration. REFERENCES
10
1. M.IC Wu et al., Phys. Rev. Lett. 58 (1987) 908.
,^
2. R.J. Cava et al., Phys. Rev. Lett. 58 (1987) 1676. 3. R.J. Cava et al., Phys. Rev. B. 36 (1987) 5719.
20
~0
60
E,mo7
FIGURE 1 Phonon density of states G(E) of YBa2Cu306.95 (1) and YBa2Cu306.3 (2) at T=80 K (dotted line) and T=290 K (solid line)
4. F. Beech et aL, Phys. Rev. B. 35 (1987) 8777. 5. M.A. Beno et al., Appl. Phys. Lett. 51 (1987) 57. 6. J.J. Rhune et al., Phys. Rev. B. 36 (1987) 2294. 7. L. Mihaly et al., Phys. Rev. B. 36 (1987) 7137. 8. I. Natkaniec et al., Letters JETP 48 (1988) 166.
The table illustrates features of G(E) in comparison with the data obtained by the neutron inelastic scattering method 6"8. model calculations 10 and optical spectroscopy data for YBa2Cu306.95 system. Comparison of available experimental results indicate
9. I.P. Eremeev et al., Study of inelastic neutron scattering in graphite at various temperatures, in Handbook: Neutron thermalization and reactor spectra, vol. 1 (Vienna, IAEA, 1968) pp. 343-360. 10. M. Stavola et al., Phys. Rev. B. 36 (1987) 850.
some difference in the spectral structure of G(E), as
11. Y. Mozioka et al., Jpn. J. Appl. Phys. 26 (1987) L1499.
well as in the position of the main features. In spite of
12. I. Bozevic et al., Phys. Rev. B. 36 (1987) 4000.
this, some similarities can be noted: peaks near 12-15
13. V.D. Kulakovsldi et al., Letters JETP 46 (1987) 460.
meV, three peaks in the range 20-30 meV, feature near 36 meV and three peaks in the high-frequency part of the spectrum (more than 40 meV). All this refers to neutron experiments, and a satisfactory agreement with model calculations is observed. Comparison with optical data indicates that it gives poor information about low-frequency part of the spectrum and rather complete information about its high-frequency part. As it follows from the optical data, the main influence of oxygen manifests itself for high-frequency part (E > 24 meV). Comparison of different G(E) spectra obtained in this work indicates that with the decrease of oxygen
14. S. Sugai, Phys. Rev. B. 36 (1987) 7133.
PHONON DENSITY OF STATES IN YBa2Cu3Ox V.G. BAR'YAKHTAR*, A.A. VASIL'KEVICH**, P.G. IVANITSKY**, V.T. KROTENKO**, A.N. MAISTRENKO**, A.E. MOROZOVSKY*, V.M. PAN*, M.V. PASECHNIK*, V.I. SLISENKO** *Institute of Metal Physic, Kiev, Ukr.SSR **Institute of Nuclear Physics, Kiev, Ukr.SSR Using the method of inelastic neutron scattering the lattice dynamics of YBa2Cu3Ox ceramics (x--6.95 and 6_3) was studied at 80 K and 290 IC The analysis of G(E) dependence revealed that with the decrease of temperature from 290 K to 80 K the noticeable changes in YBa2Cu3Ox spectrum take place, especially in the energy range above 40 meV. The reduction of oxygen concentration leads to dramatic changes in G(E) behaviour in the energy range 40-90 meV.
After establishing the superconductivity in
difference is observed at energies E=11.2, 13.7, 22.5
Y-Ba-Cu-O system 1 it was found that YBa2Cu3Ox
meV within the 36-51 MeV energy range and near 70
(x=6.95, Te=90 K) superconducting phase is an
meV.
orthorombie oxygen-deficient perovskite (sp.gr.Pmmm) 2. With the decrease of oxygen content in this system temperature of the transition into superconducting state becomes lower and when x < 6.4 the sample looses superconducting properties. Further decrease of oxygen the concentration up to x=6.2 leads
TABLE. I NEUTRON SCATTERING present work,6,7,8
16.3
one (sp.gr.P4/mmm) of order-disorder type in oxygen
18.1
sub-system at T=300 K 3"5.
17.7
7.9 14.0 14.3
18.0
18.2 19.2
20.0 22.5
23.1 23.7 124.4
conducted on time-of- flight spectrometer 9. For
25.6 25.0
obtaining the generalized density of phonon states G(E)
29.2
(in one phonon approximation) the angels of 103.3,
34.2
86.1, 70.9 were used for slow neutron scattering measurements. The average time of one spectrum
OPTICAL DATA II,12,13,1~
5.4 8.1 II.2i11.8 I0.8 12.0 13.7 15.0 14.2
to the phase transitions from orthorombie to tetragonal
Slow neutron scattering experiments were
MODEL i0
2~.2
i26.1
28.5
!27.3
25.6 27.5
36.0
31.2131.3 33.0 36.5 36.9
33.7
37 .t~ ~.9
50.0
52.7
The generalized phonon density of states G(E) for 54.6 55.5
G(E) measured at different temperature (300 K and 80 K) is observed. In case ofx=6.95 a significant
53.5 56.5
55.0
58.8
59.7
figure. One can see that with the decrease of oxygen concentration up to x=6.3 a slight difference between
39.2 41.5
~6.1 50.0
~5. o 48.0
YBa2Cu3Ox (x=6.95 and x=6.3) at T = 8 0 K (dotted line) and at 300 K (solid line) is represented in the
35.0
38.7
43.5 43.8
measurement was about 130 hours.
27.3 28.6
62.0
61.~i
70.0169.9
72.5
72.5
74./*
79.6
65.9
67.2 73.0
difference in G(E) spectra obtained for normal (T=300 K) and superconducting (T=80 K) state is seen. This
0921-4534/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland)
TABLE 1 Energies of the peaks in G(E), in meV.
76.6
V.G. Bar'yakhtar et al. / Phonon density of states YBa2Cu30~
467
content, a slight spectrum transformation at the energies less than 30 meV (except the peaks at 11.2 and 13.7 meV) and a considerable spectrum transformation i t
2o
I
at above 30 meV take place. This confirms, on one
t
/ /' ~ I
'',
hand, the essential contribution of oxygen in the high-frequency range, and on the other hand, the changes in low-frequency part imply corresponding changes of practically all strength constants resulting from the decrease in oxygen concentration. REFERENCES
10
1. M.IC Wu et al., Phys. Rev. Lett. 58 (1987) 908.
,^
2. R.J. Cava et al., Phys. Rev. Lett. 58 (1987) 1676. 3. R.J. Cava et al., Phys. Rev. B. 36 (1987) 5719.
20
~0
60
E,mo7
FIGURE 1 Phonon density of states G(E) of YBa2Cu306.95 (1) and YBa2Cu306.3 (2) at T=80 K (dotted line) and T=290 K (solid line)
4. F. Beech et aL, Phys. Rev. B. 35 (1987) 8777. 5. M.A. Beno et al., Appl. Phys. Lett. 51 (1987) 57. 6. J.J. Rhune et al., Phys. Rev. B. 36 (1987) 2294. 7. L. Mihaly et al., Phys. Rev. B. 36 (1987) 7137. 8. I. Natkaniec et al., Letters JETP 48 (1988) 166.
The table illustrates features of G(E) in comparison with the data obtained by the neutron inelastic scattering method 6"8. model calculations 10 and optical spectroscopy data for YBa2Cu306.95 system. Comparison of available experimental results indicate
9. I.P. Eremeev et al., Study of inelastic neutron scattering in graphite at various temperatures, in Handbook: Neutron thermalization and reactor spectra, vol. 1 (Vienna, IAEA, 1968) pp. 343-360. 10. M. Stavola et al., Phys. Rev. B. 36 (1987) 850.
some difference in the spectral structure of G(E), as
11. Y. Mozioka et al., Jpn. J. Appl. Phys. 26 (1987) L1499.
well as in the position of the main features. In spite of
12. I. Bozevic et al., Phys. Rev. B. 36 (1987) 4000.
this, some similarities can be noted: peaks near 12-15
13. V.D. Kulakovsldi et al., Letters JETP 46 (1987) 460.
meV, three peaks in the range 20-30 meV, feature near 36 meV and three peaks in the high-frequency part of the spectrum (more than 40 meV). All this refers to neutron experiments, and a satisfactory agreement with model calculations is observed. Comparison with optical data indicates that it gives poor information about low-frequency part of the spectrum and rather complete information about its high-frequency part. As it follows from the optical data, the main influence of oxygen manifests itself for high-frequency part (E > 24 meV). Comparison of different G(E) spectra obtained in this work indicates that with the decrease of oxygen
14. S. Sugai, Phys. Rev. B. 36 (1987) 7133.