Phase Equilibria near (Bi,Pb)‐2223, As a Function of Oxygen Partial Pressure

MacManus‐Driscoll, Judith L.; Yi, Z.

doi:10.1111/j.1151-2916.1998.tb02485.x

Cited by 13 publications

(10 citation statements)

References 25 publications

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“…Typical film thicknesses were ∼ 0.8 lm, corresponding to a growth rate of 0.02 lm min -1 . Sequential post-annealing of the pure ZnO and Zn 0.98 Co 0.02 O films were conducted in a coulometric titration annealing system [35]. Reduction annealing was undertaken at a pO 2 < 10 -11 atm.…”

Section: Methodsmentioning

confidence: 99%

Structural Evidence for Zn Intersititials in Ferromagnetic Zn_1–_xCo_xO Films

et al. 2007

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The field of spintronics has attracted significant attention since it promises new semiconductor device functionality through functionalization of both electron charge and spin degrees of freedom. Dilute magnetic semiconductors (DMS) which are formed by partial replacement of cations in a nonmagnetic semiconductor by magnetic transition metal ions are promising materials for spintronic devices since they possess charge and spin degrees of freedom in a single substance. [1] Earlier work on Mn-substituted GaAs demonstrated the potentiality of DMS materials.[2] However, the ferromagnetic transition temperature was low (T c ∼ 150 K). Theoretical predictions [3,4] of room temperature ferromagnetism (FM) in DMS has generated considerable interest in studying transition metal doped ZnO. The origin of FM in these transition metal doped oxides is not yet fully understood. Mechanisms based on carrier-induced ferromagnetism [3,4] and percolation of bound magnetic polarons [5][6][7] have been proposed. Cobaltdoped ZnO is considered to be very promising for DMS. [8][9][10][11][12][13][14][15][16][17] While there have been reports of irreproducibility of sample properties [8] as well as uncertainties about whether Co clusters are responsible for ferromagnetism, [12] there is also very strong evidence for intrinsic, ferromagnetism, and in some cases switchable, in samples made by careful chemical synthesis routes. [18][19][20] The role of defects in mediating ferromagnetism in cobaltdoped ZnO has been demonstrated by several groups. [16,20,21] The defect chemistry of ZnO is very complex, with Zn interstitials, Zn vacancies, oxygen interstitials and vacancies all known to be present in varying concentrations. [22,23] Hence, experiments to change single variables are not trivial. On the other hand, depending on processing conditions, the predominant defects are Zn interstitals and/or oxygen vacancies [24,25] and so from careful annealing studies it should be possible to distinguish the lattice variations arising from these two defect types. This paper reports on the properties of as-grown and postannealed pure ZnO and Co-doped ZnO epitaxial films grown by ultrasonic assisted solution chemical vapour deposition (UASCVD) at low temperatures. Using this method, a wide variety of doping levels are easily explored simply through changing solution composition. We show that after only one short, low temperature anneal of Zn 0.98 Co 0.02 O, M s is reduced, and at the same time so is the 'c' axis lattice parameter. The results can only be explained by a reduction of Zn concentration. Hence, measurement of the 'c' parameter provides a simple diagnostic tool for assessing whether Zn interstitials are present or not. Considering the very wide range of properties of doped-ZnO (e.g., high transparency, piezoelectricity, wide bangap semiconductivity, magnetoresistivity, magnetooptic, electro-optic and chemical sensing properties) and the need to control defects and associated charge carriers in these applications, the result of this work has br...

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Section: Methodsmentioning

confidence: 99%

Structural Evidence for Zn Intersititials in Ferromagnetic Zn_1–_xCo_xO Films

et al. 2007

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“…So far rather intuitively it has been assumed that Pb enters the Bi-22(nϪ1)n phases as divalent and therefore Pb substitution for trivalent Bi increases the concentration of holes in the CuO 2 planes. [8][9][10][11] For this intuitive view a further assumption has been made that the oxygen content remains unchanged upon Pb substitution. In this work we combine two complementary analysis techniques, i.e., x-ray-absorption near-edge structure ͑XANES͒ spectroscopy and coulometric redox titration, to show that the very simple intuitive view does not hold true for ͑Bi,Pb͒-2223.…”

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confidence: 99%

Hole doping in Pb-free and Pb-substituted(Bi,Pb)2Sr2
Karppinen
¹
,
Lee
²
,
Lee
³

et al. 2003
Phys. Rev. B
22
1
5
0
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Using single-phase samples of the (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 O 10ϩ␦ ͓͑Bi,Pb͒-2223͔ high-T c superconductor and utilizing two complementary analysis techniques, i.e., coulometric redox titration and x-ray-absorption nearedge structure spectroscopy at both O K and Cu L edges, the individual charges of the (Bi,Pb) 2 O 2ϩ␦ charge reservoir and the superconductive block that contains the three CuO 2 planes are consistently determined. Lead is found to enter the ͑Bi,Pb͒-2223 phase with a valence close to III on average. As the oxygen content concomitantly decreases, the average CuO 2 -plane hole concentration decreases upon substituting bismuth in the pristine Bi-2223 phase with lead.

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“…The key is to reduce the effective number of electrons available in the Bi-O layers for donation to the CuO 2 layers and this can be accomplished via either Pb/Bi substitution or by adding excess O. 23,24,25 In Fig. 4, the Bi-O pockets lie below E F for excess O value of δ= 0.1, but lie well above E F for δ= 0.3.…”

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Raising Bi-O Bands above the Fermi Energy Level of Hole-DopedBi2Sr2CaCu2O8+δand Other Cuprate Superconductors

et al. 2006

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The Fermi surface (FS) of Bi2Sr2CaCu2O 8+δ (Bi2212) predicted by band theory displays Birelated pockets around the (π, 0) point, which have never been observed experimentally. We show that when the effects of hole doping either by substituting Pb for Bi or by adding excess O in Bi2212 are included, the Bi-O bands are lifted above the Fermi energy (EF ) and the resulting first-principles FS is in remarkable accord with measurements. With decreasing hole-doping the Bi-O bands drop below EF and the system self-dopes below a critical hole concentration. Computations on other Bias well as Tl-and Hg-based compounds indicate that lifting of the cation-derived band with hole doping is a general property of the electronic structures of the cuprates.PACS numbers: 74.72. Hs,74.25.Jb,71.18.+y, First-principles band theory computations on the cuprates have become a widely accepted tool for gaining insight into their electronic structures, spectral properties, Fermi surfaces (FS's), and as a starting point for constructing theoretical models for incorporating strong correlation effects beyond the framework of the local-density approximation (LDA) underlying such calculations 1,2,3,4 . For example, in the double layer Bicompound Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) − perhaps the most widely investigated cuprate − the LDA generated band structure 5,6 is commonly invoked to describe the doped metallic state of the system. Band theory however clearly predicts the FS of Bi2212 to contain a FS pocket around the antinodal point M (π, 0) as a Bi-O band drops below the Fermi energy (E F ), but such FS pockets have never been observed experimentally 7 . This 'Bi-O pocket problem' is quite pervasive and occurs in other Bi-compounds. 8 Similarly, Tl-and Hg-compounds display cation-derived FS pockets, presenting a fundamental challenge for addressing on a first-principles basis issues related to the doping dependencies of the electronic structures of the cuprates.In this Letter, we show how the cation-derived band responsible for the aforemenentioned FS pockets is lifted above E F when hole doping effects are properly included in the computations. Detailed results for the case of Bi2212 are presented, where hole doping is generated either by substituting Pb for Bi or by adding excess oxygen in the Bi-O planes. With 20% Pb doping in the orthorhombic crystal structure, the Bi-O band lies ≈ 1 eV above E F and the remaining bonding and antibonding FS sheets are in remarkable accord with the angleresolved photoemission (ARPES) measurements on an overdoped Bi2212 single crystal 9 . Below a critical hole doping level, the Bi-O band falls below E F and, as a result of this self-doping effect, further reduction in the hole doping level no longer reduces the number of holes in the CuO 2 layers. We argue that the underlying mechanism at play here is that hole doping reduces the effective positive charge in the Bi-O donor layers, which then reduces the tendency of the electrons to 'flow back' and self-dope the material. We have also carried out computatio...

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Phase Equilibria near (Bi,Pb)‐2223, As a Function of Oxygen Partial Pressure

Cited by 13 publications

References 25 publications

Structural Evidence for Zn Intersititials in Ferromagnetic Zn_1–_xCo_xO Films

Structural Evidence for Zn Intersititials in Ferromagnetic Zn_1–_xCo_xO Films

Hole doping in Pb-free and Pb-substituted(Bi,Pb)2Sr2
Karppinen
¹
,
Lee
²
,
Lee
³

et al. 2003
Phys. Rev. B
22
1
5
0
View full text Add to dashboard Cite

Raising Bi-O Bands above the Fermi Energy Level of Hole-DopedBi2Sr2CaCu2O8+δand Other Cuprate Superconductors

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Phase Equilibria near (Bi,Pb)‐2223, As a Function of Oxygen Partial Pressure

Cited by 13 publications

References 25 publications

Structural Evidence for Zn Intersititials in Ferromagnetic Zn1–xCoxO Films

Structural Evidence for Zn Intersititials in Ferromagnetic Zn1–xCoxO Films

Hole doping in Pb-free and Pb-substituted(Bi,Pb)2Sr2Karppinen1, Lee2, Lee3 et al. 2003Phys. Rev. B22150View full textAdd to dashboardCite

Raising Bi-O Bands above the Fermi Energy Level of Hole-DopedBi2Sr2CaCu2O8+δand Other Cuprate Superconductors

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Structural Evidence for Zn Intersititials in Ferromagnetic Zn_1–_xCo_xO Films

Structural Evidence for Zn Intersititials in Ferromagnetic Zn_1–_xCo_xO Films

Hole doping in Pb-free and Pb-substituted(Bi,Pb)2Sr2
Karppinen
¹
,
Lee
²
,
Lee
³

et al. 2003
Phys. Rev. B
22
1
5
0
View full text Add to dashboard Cite