John E. Greedan's Research Group

Brockhouse Institute for Materials Research

Contact Information

Dr. J. E. Greedan
Dept. of Chemistry
McMaster University
Hamilton ON Canada
L8S 4M1

Office: ABB-424
Labs: ABB-436,
ABB-437, ABB-439

Ph: (905) 525-9140
ext 24725
Fax: (905) 521-2773

E-mail:
J. E. Greedan

Feedback:
comments or
suggestions

McMaster campus

Welcome

Research Themes

In our group we study the relationship between the structure and properties of inorganic solids. Our focus is on transition metal oxides (TMO's). TMO's exist in an astonishing array of crystal structures, >10³ structure types are known and hundreds of new ones are discovered each year. The crystal structure and the crystal chemistry (elemental composition, bond distances, bond angles and connectivity or topology) determine the electronic structure which in turn fixes the physical and chemical properties. TMO's exhibit a rich variety of properties from electrically insulating to superconducting, transparent to highly reflecting and diamagnetic to ferromagnetic, often within the same structural family. The physical properties can be tuned by manipulation of the crystal chemistry and, in favourable cases, very minor changes in chemistry produce major changes in properties.

It is the goal of our research program to understand these structure-property relationships in detail for selected TMO systems. We synthesize new TMO's using as much of the periodic table as possible and use the excellent and extensive facilities of the Brockhouse Institute for Materials Research and the Department of Chemistry to characterize the physical properties. We also make frequent use of national and international facilities such as synchrotron light sources and neutron sources in North America and Europe.

Detailed information on current research interests is available in the Research section.

News and Updates

Research Highlights

05/14/2007	Hello to the new summer students Sandra and Brad!
05/04/2007	Goodbye to Diego! We hope that you get a well deserved rest very soon. Good luck back in the sunny Canary Islands. Go Barcelona! (though Liverpool is better...)
04/11/2007	We have to thank Mike Malott for recent help with the webpage.

Magnetic structures of calcium manganates

The magnetoresistive "electron"-doped materials CaMnO_3-d (d = 0.06, 0.11) have been investigated by neutron diffraction. While both materials order at T_N~ 125 K, they have unique yet related magnetic structures. The CaMnO_2.94 sample orders into a simple G-type antiferromagnetic structure, shown on the left, which is also observed in CaMnO₃. The slightly more doped sample CaMnO_2.89, on the other hand, orders into a magnetic structure which is based upon the G-type, but also involves a Mn³⁺/Mn⁴⁺ charge ordering over every four layers in the crystallographic c direction (shown on the right). The potential of these kinds of materials as new magnetic recording media is great, but the mechanism for the magnetoresistive behaviour is poorly understood. Studies such as this bring us closer to this understanding, and demonstrate how subtle crystal chemistry effects can result in dramatic differences in the properties of materials. (C.R. Wiebe; J.E. Greedan; J.S. Gardner; Z. Zeng; and M. Greenblatt Phys. Rev. 2001 B64 )