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Charge-distributions in YuPr1−uBa2Cu3Ox
Physica C 235-240
(1994) 2161-2162
PHYSICA
North-Holland
Charge-distributions in Y u P r l _ u B a 2 C u 3 0 x Howard A. Blackstead, a John D. Dow, b John F. Federici, c William E. Packard, b and David B. Pulling a aDepartment of Physics, University of Notre Dame, Notre Dame, Indiana 46556 U.S.A. bDepartment of Physics and Astronomy, Arizona State University, Tempe, Arizona 85287-1504 U.S.A. CDepartment of Physics, New Jersey Institute of Technology, 161 Warren Street, Newark, New Jersey 07102 U.S.A. The charge-distributions of YuPr1_uBa2Cu3Ox with x,~7 are determined from the Rietveld-refined neutron scattering data of Neumeier et hi. using the bond-valencesum method. Differences between these charge distributions and those proposed by the Charge-Transfer hypothesis and the Fehrenbacher-Rice model are pointed out. Rietveld-refined neutron scattering data of YuPrl_uBa2Cu3Ox [1], analyzed using the bond-valence-sum method [2], yield effective charges for each of the ions, which can be compared with various theoretical models. One such model, the Charge-Transfer hypothesis [3], states that the onse~ of superconductivity in all cases is associated with the ~ransfer of holes from the Cu-O chain layers to the [CuOpj -$ cuprate planes. To test this hypothesis, we have extracted the effective charges (Fig. 1) for YuPrl_uSa2Ox with x,~7 [4]: (i) of a Cu-O chain layer, (ii) of two Ba-O layers, and (iii) of a tri-layer two-cuprate-plaae plus rare-earth "sandwich." The Charge-Transfer hypothesis implies that (i) the slopes of the lines of Fig. 1 sum to zero (they do); (ii) the 0921-4534/94/$07.00 1994 - Elsevier Science B.V. SSDI 0921-4534(94)01646-1
].0 YuPrl_oBG2Cu30, %-
~'" Ci~ain
¢D (D O~ O cO q) >., O
BG-O Layers
0.5
yer
0.0
-0.5 |
Plane Sandwich
-].0 0.0
0.2 0.4 0.6 0.8 1.0 Yttrium Content u
Fig. 1. Effective layer charges extracted from a bond-valence-sum analysis of YuPrl_uCu30 x neutron data [1].
2162
H.A. Blackstead et aL/Physica C 235-240 (1994) 2161-2162
Ba-O line has a slope of zero (it does, within experimental uncertainty); (iii) there is an abrupt change of charge at Uc, the insulating-superconducting transition composition (no evidence of it); and (iv) holes transfer from the chains to the planes as u i n c r e a s e s and one proceeds from the insulating toward the superconducting state (the slope of the chain charge indicates that electrons transfer, not holes). Particularly disturbing is the fact that the chains gain holes (not electrons) and the insulating sandwiches gain electrons as the material goes from insulating to superconducting, yet the p-type supercondactivity is supposed to originate in the initially insulating sandwiches which have been doped n-type[ Furthermore, insulating PrBa2Cu30 x has almost the same layer charges and chargetransfers as superconducting (for x>6.4) YBa2Cu30 x when the oxygen content x is varied. Thus the Charge-Transfer hypothesis is invalid, being neither a necessary nor a sufficient condition for YuPrl_uBa2Cu30 x superconductivity. Rare-earth ions on rare-earth sites do not break Cooper pairs, but a rareearth on a Ba-site does [2]. Ba-site occupancy by Pr in PrBa2Cu30 x [5] is signalled in the neutron data by the presence of oxygen at an anitchain site in a chain layer [1], and is the key to the non-superconducting character of PrBa2Cu30 x [2]. Much of what we have extracted from the neutron data conflicts with the recent theory of Fehrenbacher and Rice [81, including the following: (i) Pr acts as a pair-breaker when on the Basite, but not on the rare-earth site;
(ii) the non-superconducting character of PrBa2Cu30 7 is instrinsic and related to Ba-site occupancy; (iii) the hole concentration corresponds to about 0.51e I per unit cell in the chains of YuPrl_uBa2Cu30 x and varies some with u; and (iv) Cu+3 is absent [4]. Clearly the Charge-Transfer hypothesis and the Fehrenbacher-Rice model both require revisions, with perhaps the most important new element being that (Rare-earth)Ba2Cu30 x superconductivity originates in chain layers, with Basite pr+3 breaking Cooper pairs [4]. A c k n o w l e d g e m e n t s m We thank the U.S. Office of Naval Research, Air Force Office of Scientific Research, and Department of Energy for support (Contract Nos. N00014-92-J-1425, AFOSR91-0418, and DE-FG02-90ER45427). REFERENCES [1] J. J. Neumeier, T. Bjornholm, M. B. Maple, J. J. Rhyne, and J. A. Gotaas, Physics C 166, 191 (1990). [2] I. D. Brown and D. Altermatt, Acts Cryst. B41, 244 (1985). [3] R. J. Cava, A. W. Hewat, E. A. Hewat, B. Batlogg, M. Marezio, K. M. Rabe, :I. J. Krajewski, W. F. Peck, Jr., and L. W. Rupp, Jr., Physics C, 165,419 (1990). [4] H. A. Blackstead and J. D. Dow, Pis'ma Zh. Eksperim. Teor. Fiz. 59, 262 (1994) [JETP Lett. 59,283 (l~'~f'~A\l 1 1" 1 1 ~ ) ] and to be puonsnea. [5] P.I(aren, H.Fjellvag, O.Braaten, A. Kjekshus, and H. Bratsberg, Acta Chem. Scandinavica 44,994 (1990). [6] R. Fehrenbacher and T. M. Rice, Phys. Rev. Lett. 70, 3471 (1993).
(1994) 2161-2162
PHYSICA
North-Holland
Charge-distributions in Y u P r l _ u B a 2 C u 3 0 x Howard A. Blackstead, a John D. Dow, b John F. Federici, c William E. Packard, b and David B. Pulling a aDepartment of Physics, University of Notre Dame, Notre Dame, Indiana 46556 U.S.A. bDepartment of Physics and Astronomy, Arizona State University, Tempe, Arizona 85287-1504 U.S.A. CDepartment of Physics, New Jersey Institute of Technology, 161 Warren Street, Newark, New Jersey 07102 U.S.A. The charge-distributions of YuPr1_uBa2Cu3Ox with x,~7 are determined from the Rietveld-refined neutron scattering data of Neumeier et hi. using the bond-valencesum method. Differences between these charge distributions and those proposed by the Charge-Transfer hypothesis and the Fehrenbacher-Rice model are pointed out. Rietveld-refined neutron scattering data of YuPrl_uBa2Cu3Ox [1], analyzed using the bond-valence-sum method [2], yield effective charges for each of the ions, which can be compared with various theoretical models. One such model, the Charge-Transfer hypothesis [3], states that the onse~ of superconductivity in all cases is associated with the ~ransfer of holes from the Cu-O chain layers to the [CuOpj -$ cuprate planes. To test this hypothesis, we have extracted the effective charges (Fig. 1) for YuPrl_uSa2Ox with x,~7 [4]: (i) of a Cu-O chain layer, (ii) of two Ba-O layers, and (iii) of a tri-layer two-cuprate-plaae plus rare-earth "sandwich." The Charge-Transfer hypothesis implies that (i) the slopes of the lines of Fig. 1 sum to zero (they do); (ii) the 0921-4534/94/$07.00 1994 - Elsevier Science B.V. SSDI 0921-4534(94)01646-1
].0 YuPrl_oBG2Cu30, %-
~'" Ci~ain
¢D (D O~ O cO q) >., O
BG-O Layers
0.5
yer
0.0
-0.5 |
Plane Sandwich
-].0 0.0
0.2 0.4 0.6 0.8 1.0 Yttrium Content u
Fig. 1. Effective layer charges extracted from a bond-valence-sum analysis of YuPrl_uCu30 x neutron data [1].
2162
H.A. Blackstead et aL/Physica C 235-240 (1994) 2161-2162
Ba-O line has a slope of zero (it does, within experimental uncertainty); (iii) there is an abrupt change of charge at Uc, the insulating-superconducting transition composition (no evidence of it); and (iv) holes transfer from the chains to the planes as u i n c r e a s e s and one proceeds from the insulating toward the superconducting state (the slope of the chain charge indicates that electrons transfer, not holes). Particularly disturbing is the fact that the chains gain holes (not electrons) and the insulating sandwiches gain electrons as the material goes from insulating to superconducting, yet the p-type supercondactivity is supposed to originate in the initially insulating sandwiches which have been doped n-type[ Furthermore, insulating PrBa2Cu30 x has almost the same layer charges and chargetransfers as superconducting (for x>6.4) YBa2Cu30 x when the oxygen content x is varied. Thus the Charge-Transfer hypothesis is invalid, being neither a necessary nor a sufficient condition for YuPrl_uBa2Cu30 x superconductivity. Rare-earth ions on rare-earth sites do not break Cooper pairs, but a rareearth on a Ba-site does [2]. Ba-site occupancy by Pr in PrBa2Cu30 x [5] is signalled in the neutron data by the presence of oxygen at an anitchain site in a chain layer [1], and is the key to the non-superconducting character of PrBa2Cu30 x [2]. Much of what we have extracted from the neutron data conflicts with the recent theory of Fehrenbacher and Rice [81, including the following: (i) Pr acts as a pair-breaker when on the Basite, but not on the rare-earth site;
(ii) the non-superconducting character of PrBa2Cu30 7 is instrinsic and related to Ba-site occupancy; (iii) the hole concentration corresponds to about 0.51e I per unit cell in the chains of YuPrl_uBa2Cu30 x and varies some with u; and (iv) Cu+3 is absent [4]. Clearly the Charge-Transfer hypothesis and the Fehrenbacher-Rice model both require revisions, with perhaps the most important new element being that (Rare-earth)Ba2Cu30 x superconductivity originates in chain layers, with Basite pr+3 breaking Cooper pairs [4]. A c k n o w l e d g e m e n t s m We thank the U.S. Office of Naval Research, Air Force Office of Scientific Research, and Department of Energy for support (Contract Nos. N00014-92-J-1425, AFOSR91-0418, and DE-FG02-90ER45427). REFERENCES [1] J. J. Neumeier, T. Bjornholm, M. B. Maple, J. J. Rhyne, and J. A. Gotaas, Physics C 166, 191 (1990). [2] I. D. Brown and D. Altermatt, Acts Cryst. B41, 244 (1985). [3] R. J. Cava, A. W. Hewat, E. A. Hewat, B. Batlogg, M. Marezio, K. M. Rabe, :I. J. Krajewski, W. F. Peck, Jr., and L. W. Rupp, Jr., Physics C, 165,419 (1990). [4] H. A. Blackstead and J. D. Dow, Pis'ma Zh. Eksperim. Teor. Fiz. 59, 262 (1994) [JETP Lett. 59,283 (l~'~f'~A\l 1 1" 1 1 ~ ) ] and to be puonsnea. [5] P.I(aren, H.Fjellvag, O.Braaten, A. Kjekshus, and H. Bratsberg, Acta Chem. Scandinavica 44,994 (1990). [6] R. Fehrenbacher and T. M. Rice, Phys. Rev. Lett. 70, 3471 (1993).