Zur absoluten Präzisionsbestimmung von Gitterkonstanten mit Elektroneninterferenzen am Beispiel von Thallium-(I)-Chlorid

Abstract

A technique for the absolute determination of lattice parameters by electron diffraction is described and extensively investigated. The accuracy of the measurement of the BRAGG angle ϑ is tested with DEBYE-SCHERRER diffraction patterns. An improved technique of high-voltage measurement is used in order to obtain very accurate values of the electron wavelength λ. The discussion shows that systematic errors of Δϑ/ϑ = ± 2,5 · 10-5 and Δλ/λ = ± 1,3 ·10-5 result. Thus an accuracy of Δα/α= ± 3 · 10-5 for the lattic constant a can be claimed. This precision is comparable with that of absolute X-ray methods.The reported technique is used for absolute measurements with TlCl crystals prepared by vacuum evaporation, having lateral dimensions of about 1000 A. The lattice constant derived from (100) -, (200) - and (310) -interplanar spacings is in full agreement with the value obtained by X-ray diffraction. The remaining interplanar spacings which can be evaluated are impaired by lattice distortions and thus yield anomalous values for the lattice constant.