Single-crystal photographs

As an example of the use of single-crystal photographs for identification, vitamin B4 was shown by Bernal and Crowfoot (1933 b) to be identical with adenine hydrochloride. The extensive survey of the crystallography of substances of the sterol group by Bernal, Crowfoot, and Fankuchen (1940) gives a vast amount of information on these crystals, including unit cell dimensions this paper also contains a discussion of the identification problems in this group. 

Single-crystal photographs yielded systematic absences consistent with P6/mcc or P6cc, and the latter was chosen because of the expected alternation of A1 and P over tetrahedral nodes. 

Bodak et al. (1977) refined the crystal structure of CeRe4Si2 from X-ray single crystal photographs. Single crystals were obtained from an arc-melted button after annealing for 340 h at 800 °C in an evacuated quartz capsule. Starting materials were Ce 99.56%, Re 99.9% and Si 99.99%. 

Chevalier et al. (1982b) mentioned the existence of a compound ErjRhSi j with a structure type closely related to AlBj- The crystal strycture of ErjRhSij was refined from single crystal photographs and X-ray powder data and was found to be a superstructure of the AlBj-type according to a unit cell a — 2oo> 2co ... 

The crystal structure of ScCoo25Sii.75 (ZrSij-type) has been refined from X-ray single crystal photographs R = 0.138. The single crystal specimen was obtained from an arc-melted alloy of composition (in a/o) Sc33CogSi59. Atom ordering and parameters were Sc in 4c) 0, 0.104, 1/4 Co + 3 Si in 4c) y = 0.445 Si in 4c) y — 0.745 (Kotur and Bodak, 1977). 

Ternary phase equilibria in fig. 49a show the existence of 5 ternary silicides the crystal structures of YAl2Si and Y33 3Al452Si2o have been solved by Yanson (1975) from single crystal photographs. 

The crystal structure has been refined from single crystal photographs, = 0.115, 0.173. 

Mutual solid solubility of the binary compounds was found to be small 13 ternary compounds were observed (table 1) and the crystal structures of most of them were determined from single crystal photographs (Laue, rotation and reciprocal lattice photography). 

Determination of the crystal structure of AlB2Fc2 from X-ray single crystal photographic film data. 

KUZ] Alloys prepared by arc melting powder compacts in argon. Heat treatment at 800°C in evacuated quartz capsules 240 h. Determination of the crystal structure of Fc2AlB2 from X-ray single crystal photographic film data. 

Ross et al. [1966] have also developed systematic criteria for the identification of polymorphs based on the presence or absence of certain classes of X-ray reflections (Table 4). These criteria are unambiguous, except for two small groups of four-layer polymorphs. For their application, however, good single crystal photographs are needed, on which the reflections can be indexed with certainty. Buerger precession photographs are probably the most suitable for this purpose. 

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