ABSTRACTS OF TECHNICAL ARTICLES 1249 



Cross Sections for I on- A torn Collisions in He, Ne, and .4. J. A. Hornbeck' 

 and G. H. Wannier^. Letter to the editor. Phys. Rev., v. 82, p. 458, May 1, 

 1951. 



Ferromagnetic Resonance.*C. Kittel^ Bibliography. //. de Physique, v. 

 12, pp. 291-302, Mar., 1951. 



Theory of Antiferroelectric Crystals. C. Kittel^ References. Phys. Rev., 

 V. 82, pp. 729-732, June 1, 1951. 



Abstract — An antiferroelectric state is defined as one in which lines of 

 ions in the crystal are spontaneously polarized, but with neighboring lines 

 polarized in antiparallel directions. In simple cubic lattices the antiferro- 

 electric state is likely to be more stable than the ferroelectric state. The 

 dielectric constant above and below the antiferroelectric curie point is in- 

 vestigated for both first- and second-order transitions. In either case the 

 dielectric constant need not be very high; but if the transition is second 

 order, e is continuous across the Curie point. The antiferroelectric state 

 will not be piezoelectric. The thermal anomaly near the Curie point will 

 be of the same nature and magnitude as in ferroelectrics. A susceptibility 

 variation of the form C/(T + Z) as found in strontium titanate is not 

 indicative of antiferroelectricity, unlike the corresponding situation in anti- 

 ferromagnetism. 



Theory of Antiferromagnetic Resonance C. Kittel^ Letter to the editor. 

 Phys. Rev., v. 82, p. 565, May 15, 1951. 



Barium-Nickel Oxides With Tri- and Tetravalent Nickel.* J. J. Lander^ 

 and L. A. WootenI. ^^ Chem. Soc, Jl., v. 73, pp. 2452-2454, June, 1951. 



Abstract — The compound BaNiOa and intermediates with composition 

 ranging between BasNiaOs and Ba2Ni205 have been prepared. BaNiOs is 

 black, stable in alkali, and has a structure made up of layers identical with 

 the 111 planes of a perovskite but stacked in a close-packed hexagonal fash- 

 ion. At 730° in 730 mm. of oxygen, the structure changes to that associated 

 with the series BasNiaOg to Ba2Ni205 in which the oxygen content appears 

 to decrease continuously with temperature increasing to 1200°, at which 

 point sharp melting is observed. These materials are black and stable in 

 alkali with an hexagonal structure for which the details have not been deter- 

 mined. Resistivities and magnetic susceptibilities are reported. A wide range 

 in composition, temperature and reaction atmosphere was studied but only 

 one additional compound was observed. Attempts to isolate this compound 

 were not successful. 



The Phase System BaO-NiO.* J. J. Lander^ Am. Chem. Soc, JL, v. 73, 

 pp. 2450-2452, June, 1951. 



* A reprint of this article may be obtained on request. 

 1 Bell Tel. Labs. 



