HlD-A1350588 TDPAC (TIME DIFFERENTIAL PERTURBED ANGULAR 1/1CORRELATIONS) STUDY OF LIQUID A.. (U) OREGON STATE UNIVCORVALLIS DEPT OF PHYSICS D K GASKILL ET AL. AG NOV 83

UNCLASSIFIED TR-5 N00014-79-C-6668 F/G 7/4 N

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MICRtOCOPY RESOLUTION TEST CHARTHA1TNAL u*JRE OF STN4OARO-1963-A

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OFFICE OF NAVAL RESEARCH/CHEMISTRY

Contract N00014-79-C-0668

Task No. NR 056-721

TECHNICAL REPORT NO. 5

TDPAC Study of Liquid and Amorphous Se1 xTex AlloysNr

by0. K. Gaskill, John A. Gardner, K. S. Krane, and R. L. Rasera

Prepared for Publication

in the

Journal of Non Crystalline Solids

Proceedings of the 1983 International Conference

on Liquid and Amorphous Metals

fog pd for pub'*'

Oregon State UniversityDepartment of Physics

Corvallis, Or.

November 10, 1983

Reproduction in whole or in part is permitted forany purpose of the United States Government

LL DTICSDEC 8 30H

"TOPAC STUDY OF LIQUIJ ANI AMORPHOUS- Sel_.Te x ALLOYS*

D.K. GASKILL, JOHN A. GARDNER, K.S. KRANE, AND R.L. RASERA**

Department of Physics, Oregon State University, Corvallis, OR 97331 USA

A time differential perturbed angular correlation study on

several liquid and amorphous splat-quenched Sel xTex alloys

was performed using dilute 111Cd as the tracer. The liquid

spectra exhibits an attenuation factor, 122, consistent with

the motional narrowing approximation. The attenuation factor

is proportional to the motional correlation time tc, mul-

tiplied by the average square electric quadrupole frequency,

<VQ2>. VQ has been characterized in amorphous splat-quenched

Se and Te, allowing tc to be computed for these two liquids

from the measured 122- Spectra in both amorphous Se and Te

arise from two distinguishable sites with quadrupole frequen-

cies similar to the sites in cp! i s of Se o, Te with In.

We describe here an application of time differential perturbed angular

correlation (T)PAC) to the study of molecular dynamics in liquid Se, Te,

and Se xTe x alloys. When combined with TDPAC spectra on corresponding

amorphous solids, these measurements yield a hyperfine correlation time

t for the tracer nucleus. tc is approximately equal to the smallest of

the characteristic times of molecular rotation, chalcogenbond-breaking, or

tracer diffusion. Some of the data presented here on liquid Se and Se-rich

alloys have been described previously.1'2

The radioactive tracer used in this work was 1111n whose relevant nuclear

characteristics are given in Table 1. ,Thts.-trf decays by electron

,> l ,

MUREPORT DOCUMENTATION PAGE READ WETRUCTIONS

1.~~~2 GEA UanOoVT ACCESioN mOe. LRECIPIENT'S CATALOG HUNGER

Technical Report #514L TITLE (and S.*de) Z a.rSAf S. TYPE OF REPORT A PCNmOO COVERED

1DPAC Study of Liquid and Amorphous InterimSe1x,) All1oys 6.PERFORMING ORG. REPORT N"U911

7. AUJTHOR(@) U. ONRAC ORGRANT NUNSE1119WO)

D. K. Gaskill, John A. Gardner, K. S. Krane, N00014-79-C-0668and R. L. Rasera

V. PER1ORMING ORGANIZATION NAME AND ADDRESS 16. PROGRAM0 ELEMNT."PROJEICT. TASK

Oregon State University NR-05N6-72"1Corvallis, OR 97331 N-5-2

11. CONTROLLING OFFICE NAME AND AGGRESS It. REPORT DATE

Researc/hmsr November 10, 1983Office of Naval eac/hmity1. HUNGER OF PAGES

Arlinqton, VA 22217 1014. MONITORING AGENCY NAME A ADORESS WHOM hvlemS. COuu.S*Me151..f) I&. SECURITY CLASS (of dd e)

Unclassified

II&. 09mckd 1 IC ATOI ODOWN GRAI 14

R IS*TIMUTION STATEMENT (of .Ws Rome)L

Approve for public release, distribution unlimited

W?. OeSTINIUTION STATEMENT (W Be ubi" midio inue AW H~e AMON him Romig)

I&. SUPIPI.EMETARY NOTES

To be published in Journal of Non Crystalline Solids, proceedings of the1983 International Conference on Liquid and Amorphous Metals

W5 Kay 0OD to u~ Z Zoom 80i f 066006W m I~NtO wo MON mW)

Tim differential perturbed angular correlatit ns -

liquid Se1 Te~

amorphous Se TO'~

U.AWSRACT CC -1. 60 t0Win SWaE ima OMM OuW Sr OF.. 01161

A time differential perturbed angular correlation study on everal liquid andhous, splat-quenched Se1..xTeg alloys was performed using ilute llCd as the

racer. The liquid spectra exhi its an attenuation factor,~2 consistent withhe motional narrowing approximation. The attenuation factor is proportionalthe motional correlation time tc, multiplied by theaverage square electric

adrupole frequency, 2 .7 has been characterized: in amorphous splat-

DOI , ew1473 EDITION INV08OIIT

83 1.2 08 026W" ~ ~ 9* V -a'r Lu

---7sites with quadrupole frequencies similar to the sites in compounds of Seor To with In

oo. Teri

Atifica lon.m e (

Unittbt e,_£Y3ellt C.3

valilr,{ e .t i...

A lLk ?GI

Parent half-life 2.83 daysErwgies Of r-Y Cascade 171-24S key

Nuclear spin squence 7+ S +_ I+92 2

Anigular correlation coefficients:A22 -0 1SOJ2)

lot"uetat* nuclear state:half- life 84 nsec

spectroscopi c nuclear +0.83(13) bquadrupole moment

TAKES 1. Sumary of relevant nuclear characteristics of radioactive probe

mulide I'lln + 111Wd. All data taken from S. Raman and H. J. Kim, Nuci.

Data At, 39 (1971), except quaadrupole moment which is from-P. Herzog et

11., Z. Phys. A 2", 13 (1980).

capture to anexcited *tate of II1 Cd, ,which then decays to its ground state

by emtttq sucossiv v-rys. The emission directions of these rry

w* s trongly correlated. This correlation is perturbed if the nucleus is

Subject to 4" -external electric field gradient during the time between. the

minsion of thes f irst and second y-rays. The TOPAC measurement is intended

to deternine the time dependence of the perturbation of the angular

Liqud saples were made by placing approximately 50 mug. of the

qppiate alloy into a,3 mdiaeter quartz tube, adding a few drops of

(CeMerCally-obtained carrier-free) IIIIn-containing ICI solutiolK,

evwapratiag tk'vdtsr,, tdasting and sealing the capsule. Experimental

surmgts Were ade after the saple had been homogenized at

uxcimestiy *dC for 24 hours. these saples were not allowed to freeze

17.- Z ,.V

util te series of measurements was complete. The amorphous samples were

md by splat-quenching at A8K aind were maintained at that temperature

until all runs were complete. The experimental setup for the TOPAC

ON" uements, consists of four NaICTi) scintillation counters, arranged in

fixed positions symetrically in the horizontal plane about the sample

tureace or dewar. Delayed coincidences of the 171-245 keY cascade were

detected for interdetector angles 690A and 1600 by standard fast-slow

coincidence circuits. The resulting four spectra were stored in separate

menery banks of a multichannel analyzer computer as a function of the time

delq t betwee the two y-ray emissions. After data were collected for

appmoimately 24 hours, the ratio,

RM a2 C1(180',t) C4(180',t) 1112 - 13 C?2(90*,t) C3(90690

was computed. Htere the Ci(evt)g irni to 4, are the time spectra

collected by different detector combinations corrected for random.

coincidences. Representative R(t) spectra are shown in Figures 1-3 for

liquid $e, liquid To, and two amorphous splatsg respectively. R(t) is

related t the nuclea anisotropy A22 and the "perturbing function" 622(t)

RMt A12612(t) (2)1 *AA 22622(t)2

Toe solids, the electric field gradient is independent of time, and B22(t)

Is given by3

62 (t) In S2.0 S21~ coSsit) exp (.% 620, 2t 2)9 (3)2

wee wig 1.1 to 3 for Cd, are functions of the quadrupolar frequency

ad electric field gradient (EFG) anisotropy. 6 is a measure of the

frequency spread ~eto variations of the EFG in materials which are not

"perfect crystals. The SW 0 i, to 3, depend on the average orientation

of the EFG principal axes. Frequently nuclei occupy sites with differing

EFGs, and if so, the observed G22(t).will be the appropriately weighted sum

over all sites.

In liquids, molecular reorientation is normally rapid on the (nsec) time

scale of the measurments, and the static assumption described above is not

correct. If fluctuations are sufficiently rapid, the interaction can be

treated in the motional narrowing approximation which yields the simple

result,4

G22(t) - e " 9z (4)

where for Cd,

22 *3 2 t C <Q2> (5)250

Here tc is the hyperfine field correlation time, and <v 2> is the

average square quadrupole frequency. The data shown in Figs. 1 and 2

follow the simple exponential decay predicted by the above formula.

Significantly more structure is evident for the amorphous samples whose

spectra are shown in Fig. 3.

Fig. 4 shows the 122 values obtained by fitting the liquid data to Eq. 4.

For liquid Te, A22 could be measured accurately only in the supercooled

temperature range where it follows an activated temperature dependence with

activation energy 0.56 eV. At lowe temperatures, A22 for the Se-rich

liquids also follows an activated temperature dependence with a

c€ncentration-indepndent activation energy of 0.36 eV.

In order to compute t¢ from 12 2, <vQo> must be known. To the

extent that the average surroundings of the In/Cd tracer atom are the same

t the liquid and amorphous solid, vQ can be found from the TOPAC

V "*%

trm of the splat-quenched solid by fitting to Eq. 3. TDPAC spectra

hae ben measured only on pure amorphous Se and Te. In each case, single-

site fits were not adequate, but a two-site fit provided reasonably good

ageement with experiment. For amorphous Se, approximately 70% of the

tracer atoms we found to have quadrupolar frequency vq - 110 M'Iz and

M have vQ- 70 Piz. For amorphous To, approximately 70% have

*Q a 130M W 3M have v, a 70 M~z. a is of order 1S% for all

sites. This result indicates that in the two amorphous solids, In can

occupy sites with two different near-neighbor configurations. The

ualdrupolar frequencies of the two sites in amorphous Se and Te are

approximately the same as the frequencies of the two sites in In2Se3 and

In2Te5 respectively.5'6

With these results, <vQ2>1/2 - 100 Hz for morphous Se, and 115 M4z for

To. if <VQ2>1/2 is the same in the liquid, the correlation times for

liquid Te and liquid Se at low temperature are given by

t - va p(-E/kT), (6)

Where v- 8x101 sec "1 for Se, 2x0's sec-1 for Te, and E - 0.36 eV

for Se, 0.56 eV for To. For Se, we have previously conjectured2 that the

low temperature tc is the Cd tracer diffusion time. The prefactor for

So is consistent with this suggestion, since vO Is the correct order of

magnitude for a lattice vibration frequency. For liquid Te, tc clearly

cannot be the tracer diffusion time, since vo is much larger than

typical lattice vibration frequencies. It is presently not clear whether

ti tn To or in high-temperature Se is associated with chalcogen

bond-breaking. We hope that additional measurements on amorphous solids

ad To-rich liquid alloys my help to resolve these questions.

WFjRNCES

'Reseach supported in part by the U.S. Off ice of Naval Research.

"Pev~aent Address: Department of Physics, University of MarylandBaltimore County, Baltimore MO 21228

1)A. L. Rasera and J. Gardner, Phys. Rev. 818 (1978) 6856.

2) D. K. Baskill, J. A.,Gardner, K. S. Krane, K. Krusch, and R. L.

Rasera, in: Nuclear and Electron Resonance Spectroscoples Appliled

to Nateriols Science, eds. E. N. Kaufmann and G. K. Shenoy (North-

Holland,, PAsterda, 1981) pp. 369-373.

3) H. Frauenfelder and R. M. Steffen, in: Alpha- Beta- and Gauna-Ray

Spectroscopy, ed. Siegbahn (North-Holland, Amsterdam, 1965) Chap. 14, A.

4) A. Abraga and R. V. Pound, Phys. Rev. 92 (1953) 943.

5) L. Krtdsd' and 3. A. Gardner, Phys. Rev. 624 (1981) 4587.

6)- 0. K. BGakill to- be published.

~~ 966 C

-0.14

.v7

.74

0i o lldi'jar'. "

147j 14wtrs h

;fi i',

Is I it.t

ta'0%O

10 0 DELAY (NS) 400 13W

UN

-465

* 100 DEOLAY (NS) 40 500

Figure 2. 1(t) vs. tim for lCd Insupercooled liquid Te at 269 C (top)and *6C (bottom). The solid linesare best fits to 9quation 6

0.05

00 DELAY (NS) ;- o

Isur* 3. 1(t vs. time for 1 1 1 Cd Inamrphous splat-quenched So, (top) andTo (bottom) at 78 K. The solid linesare best fits to Rquation 3.

MikC..u Ts

31M0.m (0

Figure 4. 1 2 V11Inversetemperature forL Cd in liquidSe1,1Te allIoys.

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