Dr Isaac Abrahams

Lecturer in Inorganic Chemistry
BSc(CNAA) PhD(City) CChem MRSC

School of Biological & Chemical Sciences
Queen Mary, University of London
Walter Besant Building, Mile End Road
London
E1 4NS
Tel: +44 (0) 20 7882 3235
Fax: +44 (0) 20 7882 7427
email: I.Abrahams@qmul.ac.uk

Research Interests

1. New solid electrolytes.
 

Solid electrolytes or fast ionic conductors are a class of materials that show high electrical conductivity wholly or mainly due to the motion of ions. Devices that make use of these electrolytes include batteries, fuel cells, and gas sensors. These materials can show conduction of cations or anions but generally not both. A number of solid electrolyte systems are currently being investigated. These include cation conducting systems such as Li⁺ ion conducting phosphate glasses and anion conducting systems such as the O^2- ion conducting substituted bismuth niobates the BIMEVOX family of compounds based on bismuth vanadate.

Layered structure of BIMEVOX and details of the conduction mechanism in the vanadate layer
 
Key to development of these materials is an understanding of the structure conductivity relationship. In crystalline electrolytes this involves characterisation of the defect structure using techniques such as high resolution powder neutron diffraction. In amorphous electrolytes, because there is no long range order, other techniques such as solid state NMR and EXAFS can be used as structural probes. In both types of systems electrical behaviour is characterised using ac impedance spectroscopy.

Defect equation summarising ionic conduction mechanism in the BIMEVOX system

Diffraction techniques such as powder neutron diffraction yield an average structural picture. In order to extract information on the local defect structure the relationship between occupied sites must be examined carefully. The crystal chemistry and preferred coordination geometries for the cations must also be considered.
Taking these into account as well as partial site occupancies and short inter-site contact distances, which preclude simultaneous occupation of sites, it possible to derive cation coordination environments from the average picture generated from the structure refinement

Average Bi coordination in Bi₃Nb_0.8W_0.2O_7.1

Detail of W coordination in Bi₃Nb_0.8W_0.2O_7.1

Detail of Bi coordination in Bi₃Nb_0.8W_0.2O_7.1

Diffraction techniques such as powder neutron diffraction yield an average structural picture. In order to extract information on the local defect structure the relationship between occupied sites must be examined carefully. The crystal chemistry and preferred coordination geometries for the cations must also be considered.
Taking these into account as well as partial site occupancies and short inter-site contact distances, which preclude simultaneous occupation of sites, it possible to derive cation coordination environments from the average picture generated from the structure refinement.

2. Glasses and glass ceramics for use in hard tissue surgery
 

We are currently developing a range of calcium phosphate based glasses and glass ceramics to be used in hard tissue surgery. The advantage of this type of material is that the chemical relationship with the inorganic phase of bone is maintained. Another important advantage is that glass character can be maintained through large variations in composition. This allows for tailoring of specific properties such as mechanical strength and solubility. Structure property relationships in these systems are being examined using a variety of techniques.

[P₁₂O₃₆]^12- anion in Na₄Mg₄(P₁₂O₃₆)

In particular high resolution ³¹P, ²⁷Al and ²³Na magic angle spinning solid state NMR specroscopy has proved invaluable in structure elucidation. Excitingly, preliminary in vitro studies on these materials indicate high bioactivity with good promotion of bone cell growth.

Phosphate units observed in phosphate glasses
 

Comparison of NMR spectra between isocompositional crystalline and amorphous samples can lead to conclusions on the structure of the amorphous phase.

Comparison of ³¹P spectra for amorphous (upper) and crystalline (lower) phases of NaBa(P₃O₉)
 

In phosphate based glasses four types of phosphate environment are observed based on the number of bridging oxygen atoms surrounding the phosphorus.

Trends in ³¹P isotropic chemical shift (d_iso) with composition can also yield important structural information. For example in the glass system (0.55-x)Na₂O: xSrO:0.45P₂O₅. The variation in d_iso has been interpreted in terms of a non-random distribution of cations in the glass.

Trends in ³¹P isotropic chemical shift (d_iso) with composition in the glass system (0.55-x)Na₂O: xSrO:0.45P₂O₅
 

3. Structural studies on lone pair systems.
 

Many of the heavier main group elements exist in a subvalent form which leaves a pair of non-bonded valence electrons on the metal atom. This is commonly known as the lone pair effect and it can have dramatic effects on the stereochemistry of the resulting structures. More importantly the nature and orientation of the lone pair orbital can have an important influence on other properties in particular electronic and ionic conduction.

Isosurfaces showing the extent of the localised Wannier function associated with the non-bonding valence electron pair of Sn and Pb in (a) gas phase [SnCl₃]^-, (b) Sr(SnCl₃)₂.5H₂O, (c) gas phase [SnBr₃]^-, (d) Sr(SnBr₃)₂.5H₂O, (e) gas phase [PbBr₃]^- and (f) Sr(PbBr₃)₂.5H₂O.

We are investigating the nature of lone pair interactions in a number of systems including those containing Sn(II), Pb(II) and Bi(III). X-ray single crystal, X-ray powder diffraction and neutron powder diffraction have been used to examine the stereochemical consequences of the presence of lone pair orbitals, while electronic structure calculations employing Density Functional Theory and Hartee-Fock approximations have been used to examine details of the molecular orbitals. We have also used Wannier functions to describe the positions of the electron pairs and the degree of ionicity of the chemical bonds.

Selected Recent Publications

Defect structure and ionic conductivity as a function of thermal history in BIMGVOX solid electrolytes. I.Abrahams, F. Krok M. Malys and A.J. Bush, J. Mater. Sci., 36, 2001, 1099-1104.

Investigation of Thermal Parameters and Crystallisation in a Ternary CaO-Na₂O-P₂O₅ Based Glass System, K. Franks, G. Georgiou, I. Abrahams and J.C. Knowles, Biomaterials, 22, 2001, 497-501.

Stabilisation and characterisation of a new b _III-phase in Zr-doped Bi₂O₃, I. Abrahams, A. J. Bush, S.C.M. Chan, F. Krok and W. Wrobel, J. Mater. Chem. 11, 2001, 1715-1721.

Evidence for Cluster Orbital Formation in AB₂X₅ compounds (A = NH₄, Rb, Cs, In; B = Sn, Pb and X= Cl, Br, I), I. Abrahams, D. Z. Demetriou, R. T. Kroemer and H. Taylor, J. Solid State Chem., 160, 2001 382-387.

Electrochemical Lithium Intercalation in Lead-Tin-Aluminium Solder, A.V. Trifonova, A.A. Momchilov, B.L. Puresheva and I. Abrahams, Solid State Ionics, 143, 2001, 319-328.

Investigation of the solubility and ion release in the glass system K₂O-Na₂O-CaO-P₂O₅, J.C. Knowles, K. Franks and I. Abrahams, Biomaterials 22, 2001, 3091-3096.

Structure of Calcium Tetrasodium bis-Cyclotriphosphate CaNa₄(P₃O₉)₂ by X-ray Diffraction and Solid State NMR, I. Abrahams, G.E. Hawkes, A.Ahmed, K. Franks, J. C. Knowles, P. Bodart and Teresa Nunes, J. Chem. Soc. Dalton Trans., 2002, 1800-1805.

Structural and Electrical Correlation in BIMGVOX.05, M. Malys, F. Krok, I. Abrahams, W. Wrobel, A. Kozanecka, J.L. Nowinski, W. Bogusz and J.R. Dygas, Mol. Phys. Rep., 35, 2002, 100-104.

Solid solution limits in divalent and tetravalent substituted BIMEVOXes, F. Krok, I. Abrahams, M. Malys, W. Wrobel, A. Kozanecka, Mol. Phys. Rep., 35, 2002, 94-99.

Electrical Properties of Li₂O-SnO₂-TiO₂-P₂O₅ glasses – Identification of temperature dependent model, J.R. Dygas, K. Pietruczuk, F.Krok, E. Hadzifejzovic and I.Abrahams, Mol. Phys. Rep., 35, 2002, 150-156.

Defect Chemistry of the BIMEVOXes, Feature Article, I.Abrahams and F. Krok, J. Mater Chem., 2002, 12, 3351.

Phase Stabilisation in the Pseudo-Binary System Bi₂MgO₄-Bi₂VO_5.5-d, I.Abrahams, F.Krok, M.Malys, W.Wrobel, S.C.M. Chan, W.Bogusz and J.R. Dygas, Solid State Ionics, 157, 2003 155-161.

A Model for the Mechanism of Low Temperature Ionic Conduction in Divalent Substituted g-BIMEVOXes, I. Abrahams and F. Krok, Solid State Ionics, 157, 2003,139-145.

Phase transitions as a function of temperature in BIMGVOX, M. Malys, F. Krok, I. Abrahams, W. Wrobel, A. Kozanecka, J.L. Nowinski, W. Bogusz and J.R. Dygas, Physica Status Solidi. A, 198, 2003, 357-363.

³¹P Nuclear Magnetic Resonance and X-ray Diffraction Studies of Na-Sr Phosphate Glass-Ceramics, R.A. Pires, I. Abrahams, T.G. Nunes and G.E. Hawkes, Key Eng. Mater. 254-256, 2004, 95-98.

Stray-Field Imaging and Multinuclear Magnetic Resonance Spectroscopy Studies on the Setting of a Commercial Glass-Ionomer Cement, R. Pires, T. G. Nunes, I. Abrahams, G.E. Hawkes, C. M. Morais and C. Fernandez, J. Mater. Sci. Materials in Medicine, 15, 2004, 201-208.

Non-random cation distribution in sodium-strontium-phosphate glasses, R. Pires, I. Abrahams, T.G. Nunes and G.E. Hawkes, J. Non-Cryst. Solids. 337, 2004, 1-8.

Phase stabilisation and electrical characterisation in the pseudo-binary system Bi₂ZrO₅-Bi₂VO_5.5-d, W. Wrobel, F.Krok, I. Abrahams, A. Kozanecka, M. Malys, W. Bogusz and J.R. Dygas, Solid State Ionics, 175, 2004, 425.

A New Highly Conducting Fluorite Phase in the Bismuth Zirconium Niobate System, F. Krok, I. Abrahams, W. Wrobel, S.C.M Chan, A. Kozanecka and T. Ossowski, Solid State Ionics, 175, 2004, 335.

Structural and Electrical Characterisation of Li₂O:TiO₂:SnO₂:P₂O₅ Electrolyte Glass, I. Abrahams, E. Hadzifejzovic and J. R. Dygas, J. Chem. Soc. Dalton Trans., 2004, 3129-36

XAFS study of BIMEVOX ionic conductors for ME = Mg, Si, Zr, Zn, A. Twarog, R. Bacewicz, A. Kozanecka, W. Wrobel and I. Abrahams, Physica Scripta, T115 (2005) 318-319.

The anion disorder in the perovskite fluoride KCaF₃, D.Z. Demetriou, C.R.A. Catlow A.V. Chadwick, G.J. Mclntyre and I. Abrahams, Solid State Ionics, 176 (2005) 1571-1575.

Phase Transition Studies in BIMEVOX Solid Electrolytes Using AC Impedance Spectroscopy, I. Abrahams, F. Krok, M. Malys and W. Wrobel, Solid State Ionics, 176 (2005) 2053-2058.

Polycrystalline BIMGVOX.13 studied by impedance spectroscopy, J. R. Dygas, M. Malys, F. Krok, W. Wrobel, A. Kozanecka and I. Abrahams, Solid State Ionics, 176 (2005) 2085-2093.

Phase transitions in the BIZRVOX system, W. Wrobel, I. Abrahams, F. Krok, A. Kozanecka,, S.C.M. Chan, M. Malys, W. Bogusz and J.R. Dygas, Solid State Ionics, 176 (2005) 1731-1737.

Lone Pair Effects in Trihalo -Stannate and -Plumbate Anions in the Crystal Structures of Sr(MX₃)₂.5H₂O (M = Sn, X = Cl, Br; M = Pb, X = Br). A Joint Crystallographic and Electronic Structure Calculation Approach, I. Abrahams, D. Z. Demetriou, E. Vordemvenne, K. Mustarde and D.M. Benoit, Polyhedron, 25 (2006) 996-1002.

Multinuclear magnetic resonance studies of borosilicate glasses for use in glass ionomer cements: Incorporation of CaO and Al₂O₃, R.A. Pires, I. Abrahams, T.G. Nunes, and G.E. Hawkes, J. Mater. Chem. 16 (2006) 2364 - 2373

Defect structure and ionic conductivity in Bi₃Nb_0.8W_0.2O_7..1 I. Abrahams, F. Krok, S.C.M. Chan, W. Wrobel, A. Kozanecka-Szmigiel, A. Luma, and J.R. Dygas, J. Solid State Electrochem., in press, Online 2006, DOI: 10.1007/s10008-006-0134-y.

Last update : 14 July 2006

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