ABSTRACTS OF TECHNICAL ARTICLES 143 



quate experimental verification, that barium-strontium oxide, as used in 

 the oxide cathode, is an excess electronic semi-conductor. Accordingly, the 

 electrical conductivity of (Ba,Sr)0 has been studied as a function of tem- 

 perature before and after activation with methane, extensive precautions 

 being taken to exclude spurious effects. The increase in conductivity ob- 

 tained characterizes (Ba,Sr)0 as a "reduction" semi-conductor, and hence 

 very probably as an electronic semi-conductor whose conduction electrons 

 arise from a stoichiometric excess of (Ba,Sr) atoms in solid solution. 



A basic prediction of the semi-conductor theory has been tested quan- 

 titatively with the finding that the electrical conductivity and the thermionic 

 emission of a (Ba,Sr)0 cathode are directly proportional through three 

 orders of magnitude of activation; well-defined chemical and electrical 

 activation and deactivation procedures were used in obtaining this result. 

 It may be concluded that activation represents an increase in the chemical 

 potential of the electrons in the oxide, little or no change in the state of the 

 surface occurring. It has also been found that deviations from the propor- 

 tionality of conductivity and emission may be expected under conditions 

 leading to inhomogeneity in the oxide, in agreement with the semi-conduc- 

 tor theory also. 



Electron Microscope and Difractlon Sludy of Metal Crystal Textures by 

 Means of Thin Sections.^ f R. D. Heidenreich. Bethe's dynamical theory 

 of electron diffraction in crystals is developed using the approximation of 

 nearly free electrons and Brillouin zones. 



The use of Brillouin zones in describing electron diffraction phenomena 

 proves to be illurr. inatin j since the energy discontinuity at a zone boundary 

 is a fundamental quantity determining the existence of a Bragg reflection. 

 The perturbation of the energy levels at a corner of a Brillouin zone is 

 briefly discussed and the manner in which forbidden reflections may arise at 

 a corner pointed out. It is concluded that the kinematic theory is inadequate 

 for interpreting electron images of crystalline films. 



An electrolytic method for preparing thin metal sections for electron 

 microscopy and diffraction is introduced and its application to the structure 

 of cold-worked aluminum and an aluminum-copper alloy demonstrated. 

 It is concluded that cold-worked aluminum initially consists of small, in- 

 homogeneously strained and disoriented blocks about 200A in size. These 

 blocks are not revealed by etching but would contribute to line broadening 

 in conventional diffraction experiments. By means of a reorientation of the 

 blocks through a nucleation and growth process, larger disoriented domains 

 about l-3;u in size found experimentally could be accounted for. It is sug- 



^Jour. Applied Pliysics, v. 20. pp. 993-1010, October 1949. 



t A reprint of this article may be obtained by writing to the Editor of the Bell System 

 Technical Journal. 



