David joined the Department of Metallurgy in Oxford in September 1966 to conduct research on electron microscope images of defects in crystal lattices, under the supervision of Dr M J Whelan.

In the department of materials he “built up an outstanding electron microscopy group”, and followed up studies started in Sydney on the properties of nanometer-sized crystals (quantum dots) insemiconductor alloys.

He cared deeply about research, teaching, and university administration, and brought lucidity and commitment in equal measure to all three.” […] His interests included “theatre, music, literature, photography, travel, and bushwalking”.

[11] When he was an undergraduate at Trinity College, Melbourne University he met Jean Kerr, who enrolled a year after Cockrayne and was reading French and English honours.

She was resident in the next-door hall, and they got to know each other early in 1962 and became close friends in 1964[5] Shortly before he left for Oxford in September 1966, he proposed to Jean and they announced their engagement.

He developed the theory, and with Ray the experimental procedures for the "weak beam" technique, which improved by an order of magnitude, to 1.5nm, the resolution at which complex lattice defect geometries could be studied.

Following earlier work by Grigson, with McKenzie he developed a powerful electron diffraction technique for determining radial distribution functions from small areas of amorphous materials, collecting only elastically scattered electrons, transforming the method into a precision tool giving nearest neighbour distances accurate to 0.01A.