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Faulting in sodium azide
LETTERS
TO THE EDITOR
Faulting in sodium azide
density of extrinsic faults was in the opposite direction to that produced by intrinsic faults. (Received 25 October, 1962) If a’ is the probability of an intrinsic fault and ol” IN A recent paper KFATING and KRASNER@) is that of an extrinsic fault, then for small ECthe peak shift depends upon the difference cc’-u” reported measurements of X-ray powder pattern diffraction line shapes and positions from sodium and the broadening depends upon the sum a’+ Ed.@) Consequently, for cc’ = an, no net azide (NaNs) after various treatments. In peak shift will be observed and the broadening will particular, they noted that after deformation, the be double that from intrinsic faults only. line broadening was consistent with that expected Thus on the basis of the supposition that (i) from the formation of deformation stacking faults, extrinsic stacking faults are at least as likely to but that the anticipated shifts in the peak positions form in sodium. azide as intrinsic stacking faults could not be detected. The purpose of this and that (ii) the X-ray diffraction analysis for communication is to suggest a possible explanaextrinsic stacking faults is applicable, one can tion. explain qu~i~tively the results of Keating and Sodium azide is rhombohedral, but the structure Krasner. may also be described as hexagonal with ABCABC . . . stacking, as in f.c.c. close-packed metals. The analysis of the diffraction effects due to stacking faults was given by Keating and Krasner, and is Acknowledgement-I would like to thank the Office of Naval Research for financial support. similar to that for f.c.c. structures.@) Since there is a unique slip plane in sodium axide, no correcRlAS, Div. ofMartin Mmietta, HENRY M. OTTE tion is needed for a multiplicity of slip planes and Bal~~re, 12, the powder pattern analysis is thus simpler than Mary Zand for the f.c.c. case. References If only intrinsic (or deformation) stacking 1. KEATING D. T. and KIWNER S., J. Phys. Chem. faults are formed upon deformation or irradiation, Solids 20. 150 (1961). then the application of the analysis by Keating 2. Wm B.-E., P&r. &let. Phys. 8,147 (1959). and Krasner would be valid. However, if extrinsic P., SIEMS R. and 3. kbIlTS E., DELAVIGNETTE (or double-deformation) faults are also produced, MLINCKX S., Electron Microscopy, Academic then the expected diffraction effects would have Press, New Ydrk and London (19&j), paper B-3 (5th ~~te~tio~a~ Congressfor Electron Microscopy, to be re-examined. Published work to-date PhiZa~lphia (1962); also J_ Appl. Phys., 33, 3078 indicates that in metals, intrinsic faults pre(1962). dominate. However, in other materials, the stacking 4. JOHNSON C. A., Acta Cryst. (In press). fault energy of intrinsic and extrinsic faults may be 5. WARREN B. E., personal communication. of about equal magnitude (and possibly even less for the extrinsic faults). Such a situation appears Differential thermal analysis of yttrium iron to prevail in Si,(s) where intrinsic and extrinsic garnet faults form in about equal amounts when the material is deformed in a suitable manner. Since (Received 7 September 1962) sodium azide has a unique slip plane, the mode of deformation would not be too important in TBE USE of differential thermal analy&s (DTA) producing both types of faults if their energies techniques for the investigation of ferrites has been reported by other workers(l) but very little were approximately equal. The diffraction effects from extrinsic faults in information is available about work carried out on f,c.c. structures have recently been calculated by ferrimagnetic garnet material& especially in the temperature range above 1200°C. Technical JOHNSON.@) He found that although the same reflections were shifted and broadened as for difficulties, e.g. reactions of the sample with the intrinsic faulting, the shift produced by a low the~ocouple, electrical leakages, radiation effects, 169
TO THE EDITOR
Faulting in sodium azide
density of extrinsic faults was in the opposite direction to that produced by intrinsic faults. (Received 25 October, 1962) If a’ is the probability of an intrinsic fault and ol” IN A recent paper KFATING and KRASNER@) is that of an extrinsic fault, then for small ECthe peak shift depends upon the difference cc’-u” reported measurements of X-ray powder pattern diffraction line shapes and positions from sodium and the broadening depends upon the sum a’+ Ed.@) Consequently, for cc’ = an, no net azide (NaNs) after various treatments. In peak shift will be observed and the broadening will particular, they noted that after deformation, the be double that from intrinsic faults only. line broadening was consistent with that expected Thus on the basis of the supposition that (i) from the formation of deformation stacking faults, extrinsic stacking faults are at least as likely to but that the anticipated shifts in the peak positions form in sodium. azide as intrinsic stacking faults could not be detected. The purpose of this and that (ii) the X-ray diffraction analysis for communication is to suggest a possible explanaextrinsic stacking faults is applicable, one can tion. explain qu~i~tively the results of Keating and Sodium azide is rhombohedral, but the structure Krasner. may also be described as hexagonal with ABCABC . . . stacking, as in f.c.c. close-packed metals. The analysis of the diffraction effects due to stacking faults was given by Keating and Krasner, and is Acknowledgement-I would like to thank the Office of Naval Research for financial support. similar to that for f.c.c. structures.@) Since there is a unique slip plane in sodium axide, no correcRlAS, Div. ofMartin Mmietta, HENRY M. OTTE tion is needed for a multiplicity of slip planes and Bal~~re, 12, the powder pattern analysis is thus simpler than Mary Zand for the f.c.c. case. References If only intrinsic (or deformation) stacking 1. KEATING D. T. and KIWNER S., J. Phys. Chem. faults are formed upon deformation or irradiation, Solids 20. 150 (1961). then the application of the analysis by Keating 2. Wm B.-E., P&r. &let. Phys. 8,147 (1959). and Krasner would be valid. However, if extrinsic P., SIEMS R. and 3. kbIlTS E., DELAVIGNETTE (or double-deformation) faults are also produced, MLINCKX S., Electron Microscopy, Academic then the expected diffraction effects would have Press, New Ydrk and London (19&j), paper B-3 (5th ~~te~tio~a~ Congressfor Electron Microscopy, to be re-examined. Published work to-date PhiZa~lphia (1962); also J_ Appl. Phys., 33, 3078 indicates that in metals, intrinsic faults pre(1962). dominate. However, in other materials, the stacking 4. JOHNSON C. A., Acta Cryst. (In press). fault energy of intrinsic and extrinsic faults may be 5. WARREN B. E., personal communication. of about equal magnitude (and possibly even less for the extrinsic faults). Such a situation appears Differential thermal analysis of yttrium iron to prevail in Si,(s) where intrinsic and extrinsic garnet faults form in about equal amounts when the material is deformed in a suitable manner. Since (Received 7 September 1962) sodium azide has a unique slip plane, the mode of deformation would not be too important in TBE USE of differential thermal analy&s (DTA) producing both types of faults if their energies techniques for the investigation of ferrites has been reported by other workers(l) but very little were approximately equal. The diffraction effects from extrinsic faults in information is available about work carried out on f,c.c. structures have recently been calculated by ferrimagnetic garnet material& especially in the temperature range above 1200°C. Technical JOHNSON.@) He found that although the same reflections were shifted and broadened as for difficulties, e.g. reactions of the sample with the intrinsic faulting, the shift produced by a low the~ocouple, electrical leakages, radiation effects, 169