Professor P.D. Battle

Inorganic Chemistry Laboratory

Email Address: peter.battle@chem.ox.ac.uk

Telephone: 44 (0) 1865 272 612

1. Electronic Properties of Solids Our research interests in this area cover a number of different topics. A theme common to all of them is the attempt to correlate crystal structure with electronic behaviour, particular emphasis being placed on the link between structure and magnetic properties. Here "structure" can mean the bulk crystal structure, as determined in X-ray and neutron diffraction experiments, or the local structure around defects in non-stoichiometric materials, as studied by EXAFS, Mössbauer spectroscopy and electron microscopy. Magnetic measurements are made over the temperature range 5<T/K<300 using a SQUID magnetometer, and we can measure electrical conductivity over the same range. The ICL has three X-ray powder diffractometers, including one which can be adapted for operation with sample temperatures of up to 800 °C. In addition, high-resolution X-ray diffraction and EXAFS experiments are carried out at the Synchrotron Radiation Source at Daresbury, Cheshire. Excellent electron microscopy facilities are available in Oxford, and we also have a collaboration with the Université de Bordeaux. Neutron diffraction is carried out at the Institut Laue Langevin at Grenoble, France, or at the Rutherford Appleton Laboratory which lies fifteen miles south of Oxford. Mössbauer measurements are made in collaboration with Dr. T. C. Gibb at Leeds University. Compounds of particular interest include:

(a) oxides of elements from the 2nd and 3rd transition series (Ru, Rh, Pd, Ir, Pt) Compared to the oxides of the 1st transition series, compounds of 2nd and 3rd row transition metals have received very little attention. However, the use of 4d and 5d orbitals gives us the opportunity to increase the energy width of the valence band in oxide structures, thus moving from the localized electron regime (where compounds are insulators, often showing antiferromagnetic or ferromagnetic ordering at low temperatures) to the itinerant electron regime ( where compounds are metallic conductors and show no long-range magnetic order). We are particularly interested in preparing new compounds which lie on the border between localized and itinerant electron behaviour. In these cases we can observe the coexistence of ferromagnetism and a high electrical conductivity, both important properties in materials research.

(b) oxides containing two different d-block cations Compounds containing only one d-block cation usually order antiferromagnetically (i.e. no net magnetisation), although the spontaneous magnetisation associated with ferromagnetism is the sought-after property. The likelihood of ferromagnetic ordering is increased if two d-block cations with different numbers of unpaired electrons are incorporated into a compound, although other factors (spin frustration) have to be taken into account.

(c) incommensurate oxide structures The majority of diffraction patterns can be described using three Miller indices, hkl. However, some materials must be thought of as composite crystals in which there are two sub-structures. We are studying one such family in which the two sub-structures have the same unit cell parameters a and b, but different periodicities along z, c₁ and c₂. If the ratio c₁/c₂ is not a rational fraction, there is a mismatch between the two unit cells (an incommensurate structure) and the diffraction pattern must be described using four indices, hklm. We are trying to establish how the electronic properties of these compounds vary with the degree of structural mismatch.

(d) colossal magnetoresistance (CMR) Certain oxides of Mn are ferromagnetic below a Curie temperature, Tc. It has recently been shown that, for a subset of these compounds, the electrical resistance just above Tc decreases by several orders of magnitude when the oxide is subjected to a magnetic field. This field-induced insulator to metal transition opens up the possibility of using these manganates in devices designed to measure magnetic field strength, or to read information stored magnetically on a disk. We are preparing new manganates in an attempt to maximise this effect and to understand its origin.
The overlap between (a), (b), (c) and (d) must be stressed. For example, we have recently studied Sr₄CuIr₂O₉, a compound which falls into categories (a), (b) and (c).

2. Computer Simulation of Metal Oxide Structures This project is being undertaken in collaboration with Professor C. R. A. Catlow of the Royal Institution, London. The work involves calculations to predict cation ordering patterns and phase transitions in metal oxide structures. We have demonstrated that the energy minimisation techniques that have been used previously to model simple binary oxides can be extended to account for the properties of ternary systems. These methods are being applied to the materials (described above) that form the core of our experimental program.

We are members of an international network which has been funded by the European Community to study Spin, Charge and Orbital Ordering in Transition Metal Oxides (SCOOTMO). There are vacancies for post-doctoral research assistants wishing to work within this network: see

http://www.liv.ac.uk/Chemistry/Staff/Rosseinsky/rosseinskySCOOTMO.html

Selected recent publications

Cussen et al, J.A.C.S. 121, 3958 (1999)
Battle et al, J. Solid State Chem. 136, 103 (1998)
Battle et al, Chem. Mater. 11, 674 (1999)
Woodley et al, Phys. Chem. Chem. Phys. 1, 2535 (1999)