The microstructure of the twin to tweed transition in aluminium substituted YBa2Cu3O7-∂ single crystals

Hirst, P. J.; Drake, Alex F.; Rand, M.; Abell, J.S.

doi:10.1016/0921-4534(94)91409-5

Cited by 3 publications

(4 citation statements)

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“…W ith increasing Al content one observes a transition to the high-temperature phase at between x = 0.02 and 0.03 (figure 11), as was also found by (Drake et al 1994;Hirst et al 1994). This agrees with the discussion in §2.…”

Section: E Xam P Lessupporting

confidence: 89%

“…Experiments were performed on single crystal samples. Details of the crystal growth and thermal treatment have been published elsewhere (Drake et al 1994;Hirst et al 1994). A series of Al-doped samples were used.…”

Section: E Xam P Lesmentioning

confidence: 99%

“…The result of these measurements is in contrast to what is found in bulk spoilt. strain squared A1 content x YBa2(Cui_a;Mx)307_5, where the critical concentration of A1 has been found to be of the order of x = 0.03 (Hirst et al 1994;Lacayo et al 1992). It thus seems tha the orthorhombic phase is stabilized.…”

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confidence: 98%

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X -ray analysis of mesoscopic twin structures

Locherer

Hayward

Hirst

et al. 1996

Phil. Trans. R. Soc. Lond. A

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Section: E Xam P Lessupporting

confidence: 89%

Section: E Xam P Lesmentioning

confidence: 99%

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X -ray analysis of mesoscopic twin structures

Locherer

Hayward

Hirst

et al. 1996

Phil. Trans. R. Soc. Lond. A

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“…Halide salts are known to be effective mineralizing agents and are often used as a flux in crystal growth. 37 It is likely that the small quantity of LiF could act in a similar fashion. This raises the question of whether the fluoride ions actively enter the spinel crystal lattice or remain on the crystallite surfaces as a simple fluoride salt.…”

Section: Resultsmentioning

confidence: 99%

Microwave Synthesis of Li[sub 1.025]Mn[sub 1.975]O[sub 4] and Li[sub 1+x]Mn[sub 2−x]O[sub 4−y]F[sub y] (x = 0.05, 0.15; y = 0.05, 0.1)

Whitfield

Davidson

2000

J. Electrochem. Soc.

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Rechargeable lithium-ion batteries are becoming increasingly important as power sources for a multitude of portable consumer electronics. Currently the material of choice for the cathode material is LiCoO 2 , which although having good capacity and rechargeability, suffers from the high cost and environmental toxicity of cobalt. Consequently, much effort has been put into developing alternatives. At present, the materials most likely to succeed in future commercial applications are LiNiO 2 , LiMn 2 O 4 , LiMnO 2 , and related substituted systems. 1 Manganese-based compounds are particularly attractive due to the low cost and toxicity of manganese, so a wide range of compounds of that element has been studied. 2 LiMn 2 O 4 spinel in particular came to prominence in the early 1980s after it was demonstrated that lithium ions could be reversibly intercalated into LiMn 2 O 4 . 3,4 The material exhibits a two-stage charge/discharge at 3 and 4 V vs. Li, yielding a theoretical capacity of 296 mAh/g. However, it suffered from a number of practical problems, many of which have been overcome in the intervening years. The most troubling was the spinel's lack of long-term cyclability, shown by a marked fade in discharge capacity with cycle number. 2 This was attributed to a number of factors, including manganese dissolution, 5 electrolyte decomposition, 5 and microstructural fatigue brought about by a Jahn-Teller induced cubic-tetragonal transition. 2 Limiting the cycling to the 4 V plateau reduced but did not eliminate this structural distortion, as well as reducing the available theoretical capacity to 148 mAh/g. Substitution of some of the manganese for another element, e.g., excess Li, keeps the manganese oxidation state above 3.5 during cycling over the 4 V plateau, thus eliminating the Jahn-Teller distortion on discharge. This, together with an improved understanding of materials synthesis and processing, 6,7 has led to the achievement of good room-temperature cyclability with substituted spinel. However, its poor cyclability at elevated temperatures typically found in laptop computers, electric vehicles, etc., is an obstacle to its widespread introduction as a commercial cathode material. This mode of failure has been associated with accelerated manganese dissolution and formation of a protonated -MnO 2 phase, 8 and efforts to combat the problem have resorted to more exotic techniques than simple cation substitution.Fluorination as a means to change the structure and electronic properties of oxides became an established technique in the field of high-temperature cuprate superconductors. 9 Fluorine's ability to stabilize metastable structures made it a natural substituent in the quest for improved high-temperature storage and cycling of the lithium manganese spinels. [10][11][12] An alternative approach is the use of a barrier layer on the spinel particles to prevent contact with the nonaqueous electrolyte. 13 To date, much progress has been made, but further improvements in the elevated temperature performance of spin...

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