HIGHTEMPERATURE MAGNETIC SUSCEPTIBILITIES OF A h - 0 , AIsSE
April, 1961
the energy terms, as a good approximation; ASst* is calculated by the application of the SackurTetrode equation to give4 - Ah’str
=
In Jf
+ In T + 2.31
For argon at 77.5”1 a Faraday method3 using a Sartorious -
(3) P. W. Seh-ood, “Blagnetochemistry,” Tnterscience Publishers, New York, N. Y . , 1956. (4) N. 1’. Sidgwiok, “Chemical Elements and their Compounds,” Oxford, 1950, Vol. TI, p. 1282. ( 5 ) Swanson, e t al. NBS Circular 539, 5, 4.5 (1955), ASTM Card 7 230.
(1) Assisted by a grant by the National Science Foundation. (2) J. J. Bnnewicz, IR. F. Heidelberg and R. Lindsay. Phys. Rev., 117, 736 (1960).
,J. ,J, BANEWICZ, R.F.HEIDELBERG .&vn
H. LVXEM
Vol. 65
TABLEI THEJ$‘EISS-CURIE CONSTASTS c m AND 0 CALCULATED FROM THE EXPERIMENTAL DATAABOVE 600°K. So hZn Mn Sul,stance
Found
Theoretical
C,
6
MnO (1) 77.4 77.4 3.78 461 1.3 MnO (2) 77.1 77.4 3 68 430 1.0 MnS* A2 9 63 1 3 94 397 .. MnSe 40 9 41 0 4 02 297 1.9 AInTe 30 0 30.1 4 46 584 1.3 a A is the standard deviation of the evperimental points from the fitted line in the reciprocal molar susceptibility cersus temperature plot.
room temperature value for the gram susceptibility of MnO is considerably higher than that reported by other workers and his results therefore are 400 600 800 1000 1200 questionable. Temp., OK. The value of C, for MnSe is in good agreement Fig. 1.-Reciprocal molar susceptibilities of MnO, MnSe and with that reported by Serres.“ MnTe as functions of temperature. The constants for MnTe are between the values Mn sponge (99.9%) and ground Se (99.999%) sealed in an obtained by Serres” and Uchida.12 The value of evacuated Vycor capsule. The reaction vessel v a s heated C, is close to that expected for 5 unpaired electrons. slowly in a Bunsen burner flame to initiate the reaction. The MnSe was then further heated in an electric furnace a t 900” At around 830” the susceptibility of MnTe levels for several days. The contents of the Vycor capsule were re- off abruptly pmbably because of some sort of phase moved, ground and again heated a t 900”. The analysis of transformatioc. the final MnSe gave 40.9% Mn as compared with 41.0% The data reported here indicate that, contrary theoretical. The powder X-ray diffraction pattern showed it had a KaC1 ftructure, as previously reported,6 with “a” to the results in reference 2, as the ionic character decreases, the value of C# becomes closer to that equal to 5.457 A. The procedure followed for the synthesis of MnTe was the expected for 5 unpaired electrons. There are same as for MnSe with the substitution of Te (99.99%) several explanations which might be offered for this. for Se. Some difficulty was experienced with the Vycor reac~ ~ due to the tion vessel being attacked, in the first preparation to such an It has been suggested p r e ~ i o u s l ythat, extent that rupture occurred and the contents had to be dis- persistence of short range order, the value of CM carded. The final preparation was made in a partial helium for antiferromagnetics is to some extent a function atmosphere in a double walled Vycor vessel. The % Mn of temperature being largest close to the KBel temfound was 30.0% as compared with the theoretical 30.1 yo. perature, and becoming smaller as the temperature MnTe was found to have the PiAs structure with “a” equal increases. In this case, the value of C, observed to 4.14 A., “c” equal to 6.70 A? for a particular family of compounds in the same III. Results temperature region should increase with increasing The reciprocal molar susceptibilities versus tem- ?;Bel temperature. This is the caw for the manganese Group VI family. perature results are shown in Fig. 1. The susceptibility of MnSe was field dependent The first three members of the family, iLlnO, up to about 400”. The points shown in this region RlnS and MnSe, have the XaC1 type structure. have been extrapolated to infinite field strength. The distance of separation of the closest Mn++ ions The molar susceptibilities were corrected for the increases over 20% as the size of the negative ion diamagnetism of the constituent ions before Fig. 1 increases from 0-- to Se--. Therefore any overwas plotted. The gram ion corrections applied lap of 3d electrons which might result in partially were 26 X for MnO, 62 X for MnSe compensating spins would also decrease Kith inand 84 X for MnTe.2 Two different batches creasing negative ion size. of MnO were prepared and measured; only one It is possible to analyze the data on Rln0, MnS of these is represented in Fig. 1. and MnSe in terms of the molecular field theory of A summary of the Weiss-Curie constants ob- antiferromagnetism and estimate the exchange tained from the data above 600°K. is given in Table energies corresponding to first and second nearest I. The data were fitted to the Weiss-Curie law by neighbor interactions. For these substances, which a least squares method using a Univac Scientific crystallize in the XaC1 type structure and have 1153 computer. antiferromagnetic ordering of the second kind, the exchange energies are given by14 IV. Discussion I n the case of MnO, the Curie constant found is considerably lower than that reported by Johnston and Heikess or Bhatnagar.9 However, lower values (10) (a) Theodorides, Compt. rend., 171, 948 (1920); (b) Tyler, have been reported previously. lo Bhatnagar’s Phys. Rev.. 44, 778 (1933). E. Broch, 2. physik. Chem., 127, 446 (1927). ( 7 ) I. Oftedal, ibid., 128, 135 (1927). ( 8 ) W. D. Johnston and R. R. Heikes, J . Am. Chem. Soc., 78, 3255
(6)
(1956).
(9) Bhatnagar, Cameron, Harboard. Kapur, King and Prakash, S o c , 11, 1413 (1919).
J . Chem.
(11) A. Serres, J. phys. radium, 8 , 146 (1947). (12) Uchida, Kondoh and Fukuoka, J. Phys. Soe. J a p a n , 11, 27 (1056). (13) R. Lindsay and J. Banewics, Phys. Rev., 110, E34 (1958). (14) P. W. Anderson, ibid., 79, 705 (1950); J. S. Smart, zbzd., 86, 968 (10.52).
April, 1961
SPECTRA OF CARBON MONOXIDE CHEMISORBED o s XICKELSURFACES
617
probably considerable uncertainty in the absolute values of the J's derived by this method because it does overestimate the KBel temperature in comwhere J n n is the exchange interaction between nearest neighbors, J n n n is the exchange interaction parison with other more rigorous approximations between next nearest neighbors, IC is the Boltemann of the Heisenberg-Dirac model.l5 Despite the unconstant, B is the Curie-Weiss constant, Tn is the certainty, however, it is felt that the ratios of these NBel temperature, and Sois the spin quantum num- J ' s are a meaningful measure of the relative ber of the magnetic atom. It can be seen easily strengths of the interactions in the compounds that the ratio of Jnn to J n n n depends only on the listed. I n this connection it is interesting to note that a recent theoretical calculation by Casselman ratio of B to Tn. and KefferI6of the overlap integral between anion p3 orbitals and cation 3d oribitals (at right angles) (3) leads to a ratio of J n n / J n n n 1.5for MnO which agrees Table I1 givec; the results obtained for Jnn/'R, quite well with the value reported in Table 11. J,,,/k and J n , / J n n n when available experimental MnTe has the NiAs structure, on the other hand, data on B and T n are substituted. so perhaps it should be discussed separately. Pearson1' already has discuwed the abnormally high TABLE I1 resistivity of MnTe as compared with other compounds of NiAs group. He has suggested that the explanation for this is the lack of overlap of the 3d 3 . 3 1 . 4 3.78 4 . 9 MnO 5/2 461" 116b subshells of the Mn++ ions in this compound which 3.5 4.4 0.8 2.58 5/2 397' 154' MnS would cause it to be semiconducting instead of 0.7 7.0 0.1 M n S d 5/2 297" 247d 1.20 metallic in its properties. It is worth noting that 5/2 297" 130" 2.29 2.4 3.7 0.6 a This work. H. Bizette, C. Squire, C. Tsai and B. he has proposed a structure for hSnTe in which Tsai, Compt rend., 207, 449 (1938). Ref. 2. K. K . Mn- and Te+ ions exist involving resonating p3 Kellev, J. Am. Cliem. SOC.,61, 203 (1939). e Average of bonds with the 3d electrons of the manganese not values taken from cooling curves by: H. Bizette and B. Tsai, concerned in the chemical bonding. Compt rend., 212, 75 (1941); R. Lindsay, Phys. Rev., 84, Acknowledgment.-The authors wish to express 569 (1951). f A thermal hysteresis in the susceptibility versus temperature relation complicates the situation in their appreciation to Dr. Paul D. hlinton of the MnSe. T , on the first line of data is obtained from specific Southern Methodist University Computing Labheat data on a warming curve from 54°K. T , on the second line is estimated from magnetic susceptibility data on cooling oratory for carrying out the least squares calculacurves down from room temperature. See ref. e for further tions, and to Dr. Robert Lindsay of Trinity Coldescription of this phenomenon. lege, Hartford, Connecticut, to whom we are indebted for the section on Molecular Field Theory. The molecular field theory is the simplest approxi(15) J. S. Smart, J . Phus. Chem. Solids, 11, 97 (1939). mation of the Heisenberg-Dirac model for coopera(1G) T. N. Casselman and F. Keffer, Phys. Rev. L e t t e m , 4, 498 tive magnetic phenomena and does not take into (1960). account short range ordering effects. There is ( 1 7 ) W. B. Pearson Can. J Phys., 35, 886 ( l G 7 ) .
INFRARED STUDIES OF CARBON MOKOXIDE CHEMISORBED O N SICKEL AND ON MERCURY-POISONED SICKEL SURFACES' BY J. T. YATES,JR.,AKD C. W. GARLASD Department of Chemistry and Spectroscopy Laboratory, Massachusetts Institute of Technology, Cambridge 39, Jlassachusetts Reeezzed September t 4 , 1960
The infrared spectrum of CO chemisorbed on alumina-supported Xi surfaces has been investigated in the region from 1700 to 2400 crn.-l. Full coverage spectra clearly show that the chrtracter of the Xi surface is a function of the Xi concentration; Ni surfaces ranging from a compact crystalline type to a dispersed type have been observed. Adsorption of CO on crystalline N i sites occurs initially a t very low pressures givinq two surface species-a bridged CO between two adjacent Ni atoms, and a linear CO bonded to one surface Xi atom. 4 t higher pressures it is proposed that CO is adsorbed as a bridged CO species between Ni atoms already having adsorbed linear CO species. On more dispersed Xi sites, CO is weakly adsorbed m a single linear species and the strength of adsorption decreases as the Ni atoms become less compactly arranged. The effect of Hg poisoning of a Ni surface on the chemisorption of CO has been investigated also.
I. Introduction An infrared spectrum of C o chemisorbed on a silica-supported :Ni sample has been reported by Eischens, Francis and Pliskin,2 and Garland3 has studied the effect,of CS2 poisoning on the infrared (1) Taken from the thesis of John T. Yates, Jr., Department of Chemistry, M.I.T., in partial fulfillment of the requirements for the degree of Doctor of Philosophy. ( 2 ) R. P. Eischens, S. A. Francis and W. A. Pliskin, J . Phys. Chcm., 60, 194 (1956). (3) C. W. Garland, { b i d . , 63, 1453 (1959).
spectrum of CO adsorbed on alumina-supported Ni samples. A more extensive infrared study of co chemisorbed at room temperature on finely divided x i is reported below. The xi was supported on a high-area alumina and the concentration of T\'i in the samples was varied over a wide range (l.5-2,i70 xi by lTeight)* 11. Experimental Instrumental.-The infrared cell used in this work has been described in detail previously.4 In essence it is a cylin-
