X-RAY DIFFRACTION STUDY OF DIAMOND CONTAINING PLATELETS. G.Kowalski, J.Gronkowski, Institute of Experimental Physics, University of Warsaw, 00681, Poland and Moreton Moore Royal Holloway University of London, Egham, TW20 0EX, England

Reciprocal space maps of a natural Type Ia diamond containing impurity platelets have been measured in a four-crystal six-reflexion geometry employing a Bartels-type beam conditioner and single-bounce analyzer. The platelets lie on {100} planes: they are about 10 nm across, are a few atoms thick and, even after decades of study, excite interest because their precise composition is still unknown. [They are akin to the Guinier- Preston zones in Al-5%Cu.] Platelets are found in natural diamonds (Type Ia) which contain nitrogen; but recent studies suggest that they are not composed of nitrogen; at least, not entirely [1]. They were first directly observed by transmission electron microscopy [2]; but their presence had already been deduced from <100> spikes extending from certain reciprocal lattice points (relps) in x-ray diffraction photographs [3]. X-ray spike topography has been made quantitative: by recording intensity at angles slightly off-set from the 111 reflexion [4,5]. Studies of the 331 relp have been made by synchrotron double-crystal diffractometry and we also report here the high-resolution reciprocal space mapping around the 220 and 111 relps.

[1] G.S.Woods, in Properties & Growth of Diamond (ed. G.Davies) London: INSPEC, Inst.Elec.Eng. (1994) 94.

[2] T.Evans and C.Phaal, Proc.R.Soc.London A270 (1962) 538.

[3] K.Lonsdale, Proc.R.Soc.London A179 (1942) 315.

[4] M.Moore & A.R.Lang, J.Applied Cryst. 10 (1977) 422.

[5] S.G.Clackson, M.Moore, et al., Phil. Mag. B62 (1990) 115.