KOTES
3757
430
420
E
-
i
8
410
400
390 1.5
1.0
2.0
Log K .
Figure 3. A plot of the logarithm of t h e formation constant of the iodine complexes us. the blue-shifted iodine absorption maxima. T h e numbering of donors follows t h a t of Table I.
quinoline-iodine complex appear to be in error. Since we were able to approximate the previous results by addition of small amounts of water or simply keeping the solutions open to atmosphere for a few days, we assume that the errors were due to impurities, mainly water. It appears that when applied with precaution and under rigorous control of experimental conditions such as exclusion of water vapor, A, of the iodine complex of a heterocyclic amine can be used to estimate its pK, in cases where other methods fail. For instance, the true pK, of quinazoline has been determined only recently'o because of the difficulties resulting from the presence of covalent hydration in water solution. A pK, of 1.56 could be estimated for quinaxoline from the present data which compares with the most recent value of 1.5.
Acknowledgment. This work was supported in part by a grant from the Research Foundation of the University of Connecticut. (10) Tlr. Armareggo, J. Chem. Soc., 661 (1962).
High-Temperature Enthalpy Studies of
thalpy difference, H , - HzeOOK, was measured for Bi2S3 and SbzSes by the drop-calorimeter technique. This enthalpy difference was measured in both the solid and liquid states so that the heats and entropies of fusion of these compounds could be determined. I n addition, the enthalpy difference for Bi2Sawas extended from 400' to the melting point at 763' so that the heat capacity of Bi& could be determined over this temperature range. The only previously reported determinations of the heat of fusion and high-temperature heat capacity for BizS3 have been reported by Kelley. Kelley3 determined the heat of fusion cyroscopically and obtained a value of 8.9 kcal/mole (17.3 cal/g). He4estimated the heat capacity from free energy data and obtained a value of 28.9 6.10 X loF3!!' cal/mole deg for the temperature range 298-1000OK. In addition, Romanovskii and Tarasov5 reported low-temperature heat capacity studies (65-300'K) on a relatively impure sample of Bi&. No measurements of these thermal properties for Sb2Se3have been reported.
+
Experimental Section Calorimeter and Accessories. Measurements were made using a drop calorimeter similar to that described by Goodkin, et aL2 The temperature rise of the calorimeter was measured automatically and printed out with a digital recorder. This arrangement of electronic equipment for measuring the temperature rise consisted of a Kiethley 149 millimicrovoltmeter, which measured the emf of a copper-constantan thermocouple in the calorimeter. The output from this voltmeter was converted to a frequency by a Dymec 2210 voltage-to-frequency converter, counted with a Hewlett-Packard 52313 counter and printed out every 20 sec with a Hewlett-Packard 566A digital recorder. Materials. The samples of Bi2S3 and Sb2Se3were prepared using semiconductor grades of the elemental constituents. The sample of BizSa was synthesized using the technique described by Glatz and Meikleham6 and the sample of Sb2Se3was synthesized in a similar manner. Samples of semiconductor grade copper and silver were also employed to determine the thermal ca-
Bismuth Trisulfide and Antimony Triselenide
by Alfred C. Glatzl and Karen E. Cordo Research Diviuion, Carrier Corporation, Swacuse, N e w York (Rereiced J u n e 16, 1966)
I n the course of investigating the physical properties of certain semiconductors in this laboratory, the en-
(1) NASA Electronics Research Center, Cambridge, Mass. 02139. (2) J. Goodkin, C. Solomons, and G. Jann, Rtv. Sci. Instr., 2 9 , 105 (1958). (3) K. K. Kelley, U. S. Bureau of Mines Bulletin No. 393, U. S. Government Printing Office, Washington, D. C.. 1936. (4) K. K. Kelley, U. S. Bureau of Mines Bulletin No. 406, U. S. Government Printing Office, Washington, D. C., 1937. (5) V. A. Romanovskii and V. V. Tarasov, Soviet Phys.-Solid State, 2 , 1170 (1960). (G) A. C. Glats and V. F. Meikleham, J . Electrochem. Soc., 110, 1231 (1963).
Volume 70, Number I 1
November 1966
3758
I
I
I
I
I I
55 bHf=
0
a
I
0
-
45 u.
/ I
I I
H E A T CONTENT OF A g
a
GALIGM
II I
5
I
(3
i
\
/
0
-I
a
as-,
m
N
I: I
t-
r 25
Figure 1. Heat content for Bi& and Ag.
pacity of the calorimeter and the accuracy of the calorimetric determinations, respectively. These samples were sealed in Vycor capsules with recessed thermocouple wells which were used for measuring the temperature of the capsule in the furnace. Measureozents. Triplicate drops of the sample, the copper standard, and an empty Vycor capsule were required at each temperature so that the heat contents of the Vycor capsule and the calorimeter assembly could be determined and used for calculating the heat content of the sample at each temperature. Calculations. The calculations were performed by standard calorimetric procedures utilizing the Regnault-Ffaundlcr equation for the “cooling correction,” and were programmed in Fortran on a digital computer. Accurach and Precision. The accuracy of the heat content measurements mas determined t o be +45!&over the temperature range from 525 to 750° by comparison of the measured values of the heat content of silver (99.999 %) with those reported by Kelley.* These results are shown in Figure 1. The precision of these heat content measurements was determined to be +lye.
’
+
The Joi~rnalof Physical Chemistrv
The heats of fusion were determined from the difference of the heat contents of the liquid and solid states at the melting point and could be determined with a precision of *2%.
Results and Discussion The high-temperature heat content data for Bi2S3are also given in Figure 1 and may be represented by
H,
- H 2 g O o ~=
-11.55
+ 4.20 X 10-2T + 1.277 X 10-5T2 cal/g
over the temperature range 673-1036°K with an accuracy of *4%. From this least-squares fit of the experimental data the heat capacity over this temperature range is given by
Cp
=
4.20 X lo-*
+ 2.55 X 10-jT cal/g deg
(7) J. R. Partington, “An Advanced Treatlse on Physical Chemistry. 111. The Properties of Solids,” Longmans, Green and Co., London, 1957, p 268. (8) K. K. Kelley, U. S. Bureau of Mines Bulletin No. 584, U. S. Government Printing Office, Washington, D. C., 1960.
NOTES
3759
80
I I I
I I
70.
c
60
-
I, \ -I
a
0
8
50
I I
I I
*
I I
I
40.
--
n 0 Sb2Sea (SI
O I
I
I MELTING POINT 615OC
30.
550
500
600
650
Table I : Heats and Entropies of Fusion for Bi2S3and SbzSe3 MP, Substance
o x
Bid33
1036 888
Sb~Se3
36.90f0.74 27.00&0.54
or Cp
=
21.6
+ 13.1 X 1 O - T
cal/mole deg
If it is assumed that this equation for CP of Bi& is valid near room temperature, which appears reasonable from the experimental data given in Figure 1, the enthalpy of Bi& may be corrected to the standard temperature of 298.16OK. The corrected enthalpy of Bi2S3 referred to this temperature is given by
H, -
H298.16
=
-11.95
+ 4.20 X 10-2T
+ 1.277 X 10-5T2 cal/g
The heat fusion of Bi2S3was determined to be 36.90 f 0.74 cal/g from the difference of the heat contents of the solid and liquid states at the melting point and is shown in Figure 1. It may be observed that these
AH!, koal/mole
ASf(measd), oal/mole dee
ASf(calcd), cal/mole
18.97 f 0.38 12.97 f 0.26
18.5 14.7
18.5 25.0
deg
values of the heat capacity and heat of fusion of Bi& are significantly different from those reported prev i o u ~ l y . In ~ ~a~ similar manner, the heat of fusion of SbzSeswas determined to be 27.00 f 0.54 cal/g. These results are shown in Figure 2. The measured and calculated entropies of fusion, ASf, of Bi2S3and Sb2Se3are given in Table I. The calculated entropies of fusion were determined by assuming that the solid is completely ordered at the melting point.g It may be observed from Table I that the measured and calculated entropies of fusion for Bi2S3 agree to within experimental error while those for Sb2Se3do not. Since no low-temperature phase transi(9) 0. Kubaschewski and E. Evans, “lrIetallurgical Thermochemist r y , ” 3rd ed, Pergamon Press Inc., New York. N. Y.. 1958, pp 187-192.
Volume 70, Number 1 1
Sovember 1966
COMMUNICATIONS TO THE
3760
tions were observed on dta thermograms or have been reported for either compound, this implies that solid Bid& is completely ordered and solid SbZSe3 exhibits some degree of disorder at their respective melting points. This difference between the measured and calculated entropies of fusion for Bi2S3and Sb2Serand the difference between their measured values is unexpected, Since Bib33 and SbzSe3 are structurally similar cornpounds.1° Similar differences between the measured
EDITOR
entropies of fusion for chemically related compounds have been observed previously. l 1
A cknow&dgments. The authors wish to acknowledge the work performed by Mr. Alan Weitsman, who was employed at Carrier Gorp, as a employee in ,nc9 IJVO.
(10) E. Mooser and \V. Pearson, J . P h y s . Chem. Solids, 7, 65 (1958). (11) L. Topal and L. Ransom, J . P h y s . Chem., 64, 1339 (1960).
COMMUNICATIONS T O THE E D I T O R
Electron Spin Resonance of 016-017, 017-018,
and 018-016
Bohr magneton, and M J is the component of J along the field direction. The factor g J is given by
Sir: During the course of an investigation on the dimerization of oxygen to 0 4 , l e 4 several weak electron spin resonance peaks were observed which have not been previously de~cribed.~Xost of these were observed a t field strengths below those previously reportede6 They were at first believed to be due to the triplet state of the 0 4 species; however, the observed spectra varied with pressure in a manner identical with that of the oxygen spectra. The spectra were taken from 77 to 3OO0I
