The electrical resistivity of distilled barium from 20 ° to 400 °K

JOURNAL

OF THE LESS-COMMON

Elsevier Sequoia

S.A., Lausanne

in The Netherlands

THE ELECTRICAL,RESISTIVITY 400° Kf

M. S. RASHID

AND

Institute for Atomic (U.S.A.) (Received

January

253

METALS

- Printed

OF DISTILLED

BARIUM FROM 20” TO

F. X. KAYSER Research and Department

of Metallurgy,

Iowa State

University,

Ames, Iowa 50010

19th, 1971)

SUMMARY

Wires of barium were prepared (i) from a commercial grade of “high-purity” metal and (ii) from this material after a double distillation. The electrical resistivity (p) of the former was determined over the temperature range SO” to 300°K and of the latter from 20” to 4OO’K. The results indicate that the distillations produced a significant improvement in purity. For example, the ice-point resistivities of recrystallized specimens of the as-received and distilled materials were 34.8 and 29.4 pohmcm, respectively. The dp/dT of the purified specimen was nearly constant for temperatures from 20’ to w 140°K but took increasingly positive values at higher temperatures. A powder pattern obtained from annealed filings of the distilled metal at room temperature gave the expected b.c.c. structure with a, = 5.027 f 0.002 A.

INTRODUCTION

Barium is a member of the Group IIA family of elements which is generally referred to as the alkaline earths. It is a very reactive metal readily forming compounds with oxygen, hydrogen and nitrogen ‘*’ . It crystallizes from the melt in the b.c.c. structure and undergoes no polymorphic transformations on cooling to room temperature’. In fact, Barrett found3 that after scraping the oxide from the surface of a specimen of commercially prepared metal **, the specimen remained b.c.c. on cooling to 4.2”K. In spite of the observations summarized above, some serious doubts remain regarding the nature and properties of barium. For example, Peterson has shown that the solid metal dissolves large quantities of hydrogen4*5. Using special techniques he was able to produce specimens in which the hydrogen concentration was reduced to approximately 1 at.%. Since all published measurements appear to have been made on materials that were substantially less pure than this, it is fair to say that little, * Work was performed in the Ames Laboratory of the U.S. Atomic Energy Commission. Contribution No. 2930. ** His specimen was reported to be 99% pure with respect to metallic impurities. The concentrations of oxygen, hydrogen and nitrogen were not given. J. Less-Common

Metals, 24 (I 971) 253-257

M. S. RASHID, F. X. KAYSER

254

if any, data have been obtained from barium that could be regarded as pure with respect to the presence of BaH, and/or interstitial impurities. The research reported herein was undertaken as a first step in a proje&t “to determine selected physico-chemical properties of high-purity, strain-free specimens of barium. It is part of a larger program at the Ames Laboratory dealing with the nature of the divalent metals Ca, Sr, Ba, Eu and Yb6-‘. Commercially available metal was purified by pumping at elevated temperatures followed by distillation. All materials handling, specimen preparation and property measurements were carried out in vacuum, dry argon or helium atmospheres. We report here the initial results of experiments in which the electrical resistivity of purified barium wire was determined over the temperature range 20” to 400°K. EXPERIMENTAL PROCEDURE

Detailed descriptions of the EMHS (equipment and materials handling system) used in this investigation will be given elsewhere”*“. Briefly, this included the use of a specially designed tantalum crucible/stainless steel retort combination, a vacuum/ inert-atmosphere extrusion apparatus for preparing wire specimens, and a capsule for the wires which allowed resistance measurements to be made in an inert atmosphere or in vacuum. Each of the above mentioned apparatus was (i) a completely enclosed integral unit, (ii) made small enough to pass through the interlock of an argon box, (iii) equipped with a t 1eas t one demountable, vacuum-flanged joint, (iv) equipped with a high-vacuum valve to permit, for example, isolation and/or evacuation and refilling with another gas, and (v) baked out prior to transfer into the argon box. Allmetal systems, evacuated by sorption and ion pumps, were used exclusively in this work. Barium crown, approximately 99 wt. % pure with respect to metallic impurities, was obtained from Charles Pfizer and Company, Inc. Two bars, 0.6 cm square by 2.5 cm long were cut from the middle of the crown. One of these was extruded directly to 0.254 cm diam. wire. The other was placed in the crucible/retort combination noted above and heated in a step-wise fashion to 1120”K (at which temperature the metal was molten). During this operation the retort was dynamically pumped, the time at each temperature being of sufficient duration to reach a pressure no greater than lO-‘j torr. After the liquid had distilled onto the colder lid of the crucible, the retort was cooled to room temperature, valved off, then taken to the argon box where the distillate was charged into a second crucible. The distillation was repeated as before. The crystals collected the second time were charged into a small tantalum capsule which was immediately electron-beam welded closed. The capsule was placed in a retort which was subsequently evacuated to low6 torr, heated to 1040°K, held at this temperature for 12h with the barium molten, and then cooled to room temperature. The ingot obtained was extruded to 0.254 cm diam. wire. All of the wires were of superior quality, possessing lustrous surfaces and highly uniform cross-sections. Wire specimens, approximately 3 cm long, were used for the electrical resistance measurements. Welding of the current and potential leads and encapsulation of the specimens were carried out in the argon box. A copper-constantan thermocouple was either welded to the specimen or placed in close proximity to it in the capsule. The argon in the capsule was replaced with helium in order to insure the presence J. Less-Common

Metals, 24 (1971) 253-257

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of a vapor phase at the lowest temperatures. The d.c. electrical resistance of the specimen was measured potentiometrically using a regulated current supply and the standard current reversal technique. All of the resistivities reported here were calculated on the basis of specimen dimensions taken at room temperature. Resistance measurements were made with a given specimen first in the asextruded and then in the recrystallized condition. The recrystallization treatment, 16 h at 470” K, was effected with the specimen in the (gas-filled) capsule. Measurements between 300” and 77.4’K were made in a liquid nitrogen cryostat. Those below 77.4”K were made in a liquid helium cryostat. A stirred glycerin bath was used at temperatures above 3OO’K. Uniform rates of heating and cooling were easily obtained above 77.4”K and there was little thermal gradient in the specimen. Measurements from 20’ to 77.4’K were taken on heating only because of difficulty in controlling the cooling rate in the liquid helium cryostat. Minus 200 mesh tilings were prepared under argon from the doubly distilled wire. These were sealed in Lindeman capillaries and annealed at 400°K for 4 days. An X-ray powder pattern was obtained of the specimen at room temperature using a 114.6 mm diam. Debye-Scherrer camera and filtered copper radiation. The lattice parameter was determined using a computer program which performed a weighted least squares analysis and assumed the systematic errors to follow the TaylorSinclair/Nelson-Riley function”. I

I

56

16

Fig. 1. The temperature dependence of the electrical resistivity of several barium wires : (1) commercially available metal as-extruded, (2) same specimen as (1) but after 16 h at 47@K, (3) wire prepared from ingot of doubly distilled metal. .I. Less-Common

Metals, 24 (1971) 253-257

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M. S. RASHID, F. X. KAYSER

EXPERIMENTAL RESULTS AND DISCUSSION

The temperature dependence of the electrical resistivity, p(7), of specimens prepared from the distilled and as-received materials is shown in Fig. 1. Since these particular specimens exhibited no hysteresis on heating and cooling, no differentiation is made between data points taken with respect to increasing or decreasing temperature. Curve 1 represents p(T) of the as-received metal, in the as-extruded condition, over the temperature range 93” to 300°K. The p(T) of the same specimen after the recrystallization treatment is indicated by curve 2. It can be seen that these two curves are essentially parallel and exhibit a positive valued d2p/dT2, and also that the recrystallization treatment produced a dp z - 2.5 pohm-cm. The data obtained from the wire of doubly distilled barium are illustrated by curve 3. The fact that this curve lies below the other two is taken as evidence that the distillations improved the purity of the as-received metal. When measurements were repeated after annealing this specimen for 16 h at 470”K, no change was noted. Apparently, the increase in purity lowered the recrystallization temperature to near room temperature. Curve 3 is nearly linear for temperatures up to m 140°K but for higher temperatures a positive valued d2p/dTZ is again observed. The resistivity of this wire at 20” K ( + 4”) was 0.13 pohm-cm. The resistivity ratio, p (300” K)/p (4.2”K), must therefore be greater than 250. Its most probable value is in the range 400 to 900. Because of the formidable problems of working with barium (even with present day technology), only a few investigators have examined the temperature TABLE I X-RAY DIFFRACTION DATAOBTAINED

FROMFILINGSOFDISTILLED

BARIUM AT298°K

hkl 110 200 211 220 310 222 321 400 330,411 420 332 422 510,431 521 440 433,530 442, 600 532,611,, 532,611,,

*

k,,

is

the

0.0473 0.0943 0.1415 0.1891 0.2360 0.2828 0.3300 0.3779 0.4235 0.4714 0.5181 0.5647 0.6120 0.7054 0.7543

VS

m S

m m W m W m W W vvw VW “VW vvw vvvw vvvw

0.8929 0.8961 a,, = 5.027 f 0.002 A k,=4.39 x lo-“ (*)

VW VW

systematic

errors

constant.

J. Less-Common Metals, 24 (1971) 253-257

0.0474 0.0946 0.1417 0.1888 0.2358 0.2829 0.3299 0.3770 0.4240 0.4710 0.5180 0.5650 0.6120 0.7060 0.7530 0.8006 0.8476 0.8925 0.8969

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BARIUM

dependence of its electrical resistance I%* . Of these, only Rinck employed specimens of sufficiently uniform dimensions to permit the calculation of resistivities”. His measurements, made over the temperature range 273.2” to 85O“K, provide data with which the present results can be compared. The comparison suggests that the EMHS used in the present work resulted in higher purity specimens than those available to Rinck. For example, values taken from his p(T) curve at temperatures of 273.2”, 300” and 400” are 36.0, -41 and N 67 pohm-cm, respectively. Values taken from Fig. 1, curve 3, at the same temperatures are 29.4,33.2 and 55.6 pohm-cm. We note also that Rinck’s curve showed a positive value of d2p/dT2 for temperatures up to about 650°K. The results obtained from the powder pattern are listed in Table I. The pattern indexed as b.c.c. with a lattice parameter of 5.027 f 0.002 A. The latter is essentially the same as that reported by others. For example, a listing of published room-temperature lattice parameters for barium cited values of 5.023,5.016,5.02 and 5.025 A16. A number of weak, low-angle lines were present in the patterns obtained in this investigation (these are not included in Table I). They were tentatively indexed as BaO and BaH,. It is possible that the contamination was a result of annealing in quartz capillaries and/or filing. However, it remains to be shown that this was the case. ACKNOWLEDGEMENTS

The authors wish to thank Mr. Gaylord Stowe for important help in all phases of this investigation. We are also indebted to Mr. F. N. Linder for performing the electron beam welding. REFERENCES 1 M. HANSENANDK. ANDERKO,Constitution ofBinary Alloys, McGraw-Hill, New York, 2nd edn., 1958. 2 W. B. PEARSON,Handbook of Lattice Spacings and Struqtures of Metals and Alloys, Pergamon Press, New York, 1958. 3 C. S. BARRETT,J. Chem. Phys., 25 (1956) 1123. 4 D. T. PETERSON AND M. INDIG, J. Am. Chem. Sot., 82 (1960) 5645. 5 D. T. PETERSON AND C. C. HAMMERBERG, J. Less-Common Metals, 16 (1968) 451. 6 F. X. KAYSERAND S. D. SODERQUIST, J. Phys. Chem. Solids, 28 (1967) 2343. 7 S. D. S~DERQUIST AND F. X. KAYSER,J. Less-Common Metals, 16 (1968) 361. 8 F. X. KAYSERAND S. D. SODERQUIST, Scripta Met., 3 (1969) 259. 9 F. X. KAYSER,Phys. Rev. Letters, 25 (1970) 662. 10 F. X. KAYSERAND M. S. RASHID,to be published. 11 F. X. KAYSERAND M. S. RASHID,to be published. 12 F. X. KAYSER,to be published. 13 G. T. MEADEN,Electrical Resistance of Metals, Plenum Press, New York, 1965. 14 W. KLEMENTAND A. JAYARAMAN,Progress in Solid State Chemistry, Vol. 3, Pergamon Press, Oxford, 1966. 15 E. RINCK, Compt. Rend. Acad. Sci. (Paris), 193 (1931) 1328. 16 U.S. Bur. Standards Circ. 539, Vol. IV, 1955, p. 7.

* See Ref. 14 for a listing of resistance change under pressure.

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