Prosiding Pertemuun Ilmiuh Suins Materi III..\'erpong, 20 -21 Oktober 1998 ISSN 1410-2897

PRELIMINARY STUDY ON SICG(AgI)x(AgPOJ)t-x BY NEUTRON SCATTERING

s.?:6

E. Kartinil, P. Tri Hardil , S. YusuP, Setiawan1, H. Mugy RahardjolN. Indayaningsih2, S.J. Kennedy

IMaterials Science Research Center,BATAN, Indonesia2Indonesian Institute of Science, Indonesia

3Australian Nuclear Science and Technology Organization, Australia

ABSTRACT

PRELIMINARY STUDY ON SICG (Agl)x(AgPO3) BY NEUTRON SCATTERING. Samples of superionic conductorglasses with phospate glass system (AgI)x(AgPOJ have been made for some compositions (x). The glass material is made froma mixture of AgNO) and (NH4)HzPO 4 acting as glass network and AgI as a dopant salt which forming superionic properties. WithAgi compositions ofx=O.O. 0.3. 0.5, 0.7 the samples were characterized with neutron scattering technique using High ResolutionPowder Difractometer (ON3). Data were collected at a neutron wavelength of 1.21 A using Ge(311) monochromator. Thesuperionic glasses data were corrected with vanadium can data, absorption and transmision factor of the samples. From theanalysis results obtained that a main peak with large broadening appear around Q=5.6 A.I and a first sharp diffraction peak(FSDP) appears around QcJ A.I. The FSDP intensity increase with increasing Agi composition which is doped into glassnetwork AgP°l.

ABSTRAK

STUDI PENDAHULUAN SICG: (Agl).(AgPO),-. DENGAN HAMBURAN NEUTRON. Telah dibuat cuplikanbeberapa gelas konduktor superionik dengan sistem gelas pospat (AgI)x(AgPO)).-. untuk beberapa komposisi (x) .Bahan gelasAgPO) dibuat dari campuran AgNO) dan (NH4)HzPO4 sebagai jaringan gelas (glass network) clan AgI sebagai garam dopanpembentuk sifat superionik. Cuplikan dengan komposisi AgI sebesar x=O,O, 0,3, 0,5 clan 0,7 cuplikan dikarakterisasi denganteknik hamhuran neutron menggunakan Difraktometer Neutron Resolusi Tinggi (ON3). Data diambil pada panjang gelombangneutron 1.21 A dengan menggunakan monokromator Ge(311)- Data gelas konduktor superionik ini dianalisis dengan memasukkanfaktor koreksi wadah vanadium, faktor serapan dan faktor transmisi cuplikan. Dan hasil analisis diperoleh puncak utama dengansebaran yang cukup lehar disekitar Q=5,6 A-I dan sehuah puncak difraksi tajam pertama (FSDP) pada daerah sekitar Q< lAIntensitas FSDP ini naik dengan naiknya komposisi garam AgI yang ditambahkan ke dalam jaringan gelas AgPO,

INTRODUCTIONity in AgI doped glasses. AgI is, in its crystallinealpha-phase above 147 .C, one of the best ionic con-ductors known.

In this paper, the structure factor of superionicconductor glass (AgI)x(AgPOJi-x observed by a neu-tron diffractometer will be reported. The 'glass' com-ponents are phosphate chains and the main dopant saltsare AgI with various compositions.

Neutron Diffraction Method

.In neutron diffraction investigations, a neutronbeam is monochromated by Bragg reflection from acrystal. The wavelength of the neutrons incident uponthe sample can be changed by adjusting the scatteringangle of the monochromator. The scattered neutronsare measured by means of counter that can be rotatedabout the sample. The necessary resolution is obtainedusing collimators. These collimators are located at theprimary beam before the monochromator, between themonochromator and the sample, and before the detec-tor. The monochromator is surrounded by a radiationshield to protect the experiment and experimenter from

The interest in glasses with high ionic conduc-tivity is growing rapidly because of their potentialapplications as solid electrolytes in new electrochemi-cal devices such as solid state batteries. fuel cells andchemical sensors. Many different kinds of amorphousionic conductors with conductivities comparable tothose in liquid eletrolytes have been structurally inves-tigated. Wit11 the aim of understanding the diffusionmechanism. which occurs in a relatively frozen envi-ronment (1-3).

Several models have been developed to explainhow the ionic conduction mechanism occurs when thedopan salt is added to the supporting glass. In onemodel (4], it is proposed that the metal halide salt isintroduced into the amorphous network in clusters ormicro domains of size> 10 A. Within the micro do-mains. which are assumed to have an internal struc-ture similar to t1\at of the dopant salt, the barriers forconduction are low whereas t1\ere may be relativelyhigh berriers between clusters. This model has beenused in particular to explain the high ionic conductiv-

Prosiding Pertemuan Ilmiah Sains Materi IIISerpong, 20 -21 Oktober 1998 ISSN 1410-2897

der diffractometer. The experimental conditions werechosen using a low take off angle at the monochroma-tor to obtain lower wavelength with the highest inten-sity. A gennanium monochromator (311) at the wave-length of 1.21A was used for the experiment. This neu-tron wavelength was chosen to obtain wide range ofQ. The scattering was recorded using 32 detectors atthe scattering angles ranging from 2.5 to 162.5°, with 28steps of 0.25°. The wavenumber Q values were ob-tained between 0.25 to 10.22 A -I. The measurementswere carried out at room temperature for the glass com-positions of x = 0, 0.3, 0.5 and 0.7. An identical empty

vanadium was also measurro within the same conditionsas for those glass measurements.

fast neutron and gamma radiation.The scattering vector Q is derived from the

Bragg equation, I = 2d sin e , so that

Q 4trSinfJ = (1)).

where A and e are the neutron wavelength and braggangle, respectively. For Bragg scattering the incomingand outgoing wave vectors have the same magnitude,k = k'. Although for Bragg scattering k = k' and ro =

0 exactly, the scattering from a liquid involves energytransfer ( ro :#: 0 ). In a powder instrument the detectorintegrates over the energy of the neutrons scatteredthrough 28 angle. This integral is not at constant Q sothat it does not strictly give the scattering function S(Q).However if all the weight of the integral is at lowfrequency, i.e. lllO« 1l2k2 /2m , then what ismeasured is over very small range of Q and can bereasonably equated with S(Q). This is known as thestatic approximation which is good for the quasielasticpart of the scattering from a liquid.

DATA CORRECfIONS

The corrections of the neutron diffraction dataon SICG will be d~bed in this section. There are threecorrections namely, the corrections made for absorp-tion, for the scattering from the empty sample holderand for relative efficiency of various detectors.

EXPERIMENTAbsorption con-ection

Sample Preparation There are severn! steps in calculating the absorp-tion or transmission correction factor. Those are calcu-lating the number of molecules per unit volume n ofthe sample, calculating the total actual cross section0"1o1al and calculating the transmission factor T(8) or ab-sorption factor A(8).

Calculating the number of molecules per unitvolumes n

The chemical fonnula is AgIx(AgPO3)I-x and thecross section data for each of the constituent atoms aregiven in Table I

Tabel 1. Cross section data AgI.(AgPO,),-,

The number of molecules per unit volume n(x) as afunction of x (molar percents AgI ) is calculated fromthe following relation

n(x) =p(x) / W(x) (2)

where (w(x» is the fonnula unit mass of AgIx(AgP°3).-X'and p (x) is the mass density (see Table 2).

Glass (AgI).(AgPO)t-. systems were preparedwith molar dopant concentrations of 0, 30, 50 and 70% AgI, according to the following procedures. The rawmaterials AgI (Merck 99.98% ) was first purified anddried before mixed together with the other component.Usually the raw AgI has three different structures,namely a-r3-y phases. In order to obtain the r3-phasewe need to purify the AgI by dissolving it in a highlyconcentrated solution KI, then the mixture was fil-tered in a light concentrated solution KI. The r3-AgIthen was dried in an oven at 90°C for about twenty fourhours, then allowed to cool in a dessicator before used.Appropriate amounts of AgNO) and (NH4)~PO 4 wereweighted, mixed and ground together. The mixturesin porcelain crucibles were heated gradually(100°C/h) to a temperature of 700°C. The melt was keptat this temperature for 2 hours. The glass specimenswere made by pouring the melts into a cylindrical rodteflon with 5mm diameter and 57 mm length, and thenwas quenched in liquid nitrogen. A clear glass was ob-tained and the colour became yellowish when more AgIconcentrations were added. A small cluster of AgI ap-pears in the glass specimen as the concentration of AgIincreased. The rod-casted glass was then moved intoa cylindrical vanadium can with diameter 5.5 mm andlength 62 mm for neutron diffraction experiment.

Diffraction MeasurementCalculating the total cross section of the sample

Experiments were performed at the NeutronScattering Laboratory, Materials Science Research Cen-ter, BATAN. Indonesia using a high resolution pow-

The neutron wavelength of this experiment wa~1.21 A, which corresponds to the velocity ofvo = 3.26km/s .The absorption cross section in Table I (for the

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Prosiding Pertemuan llmiah Sains Materi IIISerpong, 20 -21 Oktober 1998 ISSN 1410-2897

Tabel 2. The macroscopic data of AgI.(AgPO,),o.

iliqxNtionx

DnityI:(x)

Tctal~miooO"t(x) (lml)

0

03

4.4853-5.0045

5.3~

-siiij;

.AJ:mic

\\t:i{jt~1&1838

M:i00.ll~/\durre

r(x)0.0725 35.4&1

3294]9

3].44]

.'Jl (Jl] 2.

TrnIH1i~mrajaT(x)

O.77J7

0.7814

Al:aJ]1imf/Xi{r

A(x)1.2924

1.27~J:>1.2A77

210.&S35

m.4593

O.<X>119

0.5 0.05:k55

0.01611

o.~ 1.2716

0.7 0.7914 1.2637

Maxwellian distribution) is for neutron with velocity v= 2.2 km/s. Therefore the absorption cross section G'obs(v = 1.6689 km/s) is

0

x, respectively. D(e) is a multiplication factor ofdetectorefficiency as a function ofe. The absorption A(x) andthe transmission factor T(x) vary with composition x, astabulated in Table 2.

cr' L- (v = 1.6689km/s) = (2.2/3.26) crb.~ 0 ..

(v = 2.2 km/s) (3) RESULTS

Table 2 shows that densities and transmissionfactors of the samples increase with increasing com-positions of the salt dopant AgI. Figure 1 shows a neu-tron diffraction pattern of AgP°3 .Figure 2 shows theneutron diffraction pattern for AgPO3, (AgI)o3

(AgPO3)O7 ' (AgI)os(AgPO3)o.s' (AgI)ojAgPO3)o3.Eventhough the statistic was not very good, each pat-tern does show Seatures typical to amorphous materi-als. The diffraction patterns consist of several broadpeaks with width increasing as Q increases. Thesebroad peaks are at Q values of 1.98,3.10,5.60 and 8.09A.I for x=O.O, 0.3, 0.5 and 0.7 compositions respec-tively. The first sharp diffraction peak (FSDP) is ob-served at Q < lA-I. This FSDP only appears for salt

doped ,in particular a FSDP at Q <I A-I grows andbroadens as the salt is added more.This broad peak arises from several ion pair separationsuch as Ag-Ag, Ag-p' Ag-O, P-P and P-O of the phospatenetwork glasss in which the four broad peaks arepronounced. There is not much observed peaks at higherQ and the rest of the diffraction pattern are mostly flat

The total cross section of the AgIx(AgPO3)I-x performulaunit is

(]" tota! = [~(]" inc(i) + (]" coh(i) + (]"~s(i)]X N(i) (4)

where N(i) is the number of atoms of type i in the

formula unit.

Calculating the transmission factor

The transmission factor can be determined via

I(fJ)T(fJ) = /]0) = exp( -,uR) (5)

where 1(8) is the measured intensity, including thetransmission, absorption and scattering intensities,which depends on the scattering angle 8. R is the radiusof the sample, and in this experiment R is 0.25 cm.J.I.(x) = n(x) cr, (x) is the linear absorption coefficient in

cm-l. It is often convenient to replace the transmissionfactor T(EI) by the absorption factor A(EI) = T-I(8) i.e the

number by which the apparent intensity should bemultipl.ied to get the true intensity. The transmissioncorrection factors for successive values of x are tabulatedin the Table 2. The absorption correction factor A(EI) isonly weakly dependent on the scattering angle.

Empty-Vanadium Correction

In addition to the measurements of the scatter-ing from SICG plus the sample holder, we also mea-sured the scattering from an empty sample holder atroom temperature, since the measured data has to becorrected by using the relation

I,(e,x) = A(x)D(e){Im(e,x)- T(x)Iv(e;x)} (6)

where I.(8,x), Im(q,x),Iv(8,x) are the scattering intensitiesof the sample, the measured data and the empty vanadiumcan as a function of scattering angle 28 and composition Figure I. Neutron Diffraction pattern of AgPO]

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Prosiding Pertemuan Ilmiah Sains Materi 11/Serpong, 20 -21 Oktober 1998 ISSN 1410-2897

data[2]. The intensity changes of the first sharp dif-fraction peak are closely related to the increasing ofionic salt AgI doped into the glass phospate substrate.The peak becomes higher as the AgI concentration isincreased. but not for the main diffraction peak. How-ever. there is still being debated whether the develop-ment of the first sharp diffraction peak arises from theionic conductivity in the sample. or only from its ionicbonding. The SICG becomes partially crystalline as theAgI is added more to the glass substrate. as shown inFigure 1 for the AgI molar composition 70%. It is inter-esting to observe the nucleation process of this mate-rial. by either to increase the doping salt or by heatingthe materials for insitu measurements.

ACKNOWLEDGMENT

The authors would like to thank Dr. A. Ikram(Head of Neutron Scattering Laboratory). and Dr. MFCollins (Dept. of. Physics, Mc.Master University,Canada). This work was partially supported by aGrand-in-Aid from National Research Council of In-donesia, the Materials Science Research Center,BATAN and the National Science and EngineeringResearch Council of Canada.

Figure 2. Neutron Diffraction patem of (AgI).(AgPO,),...The diffraction paterns for a, b., c. d in thefigure indicated to x=O. 0.3. 0.5 and 0.7 respec-tively

[2). In tenDS of the atomic scattering amplitudes. neutrondata are more strongly weighted towards the networkcomponent (P and 0). At higher Q the neutron diffi"actionpatterns for doped and undoped glasses are similar. sincethis depends mostly on the short range covalent bonding,which is therefore largerly unchanged by addition ofsalt. However for AgI doping are large changes at low Qand main diffraction peak at Q» 5.6 A-I decreases andgets smaller as AgI content increases. There is littlechange in other Q values.

REFERENCES

CONCLUSIONS

Some samples of superionic conductor glassbased on phosphate glass system have been madesuccesfully. This preliminary study of superionic con-ducting glasses of (AgI)x(AgPOJ)l-X series with x=O, 0.3,0.5 and 0.7, performed at Neutron Scattering Laboratoryin Indonesia, gives a promising sign that a further ex-periment can be conducted here as long as the statisticcan be improved. Even with bad statistic data of thesample, it shows that our samples had good quality.This can be seen from several-pronounced peaks andtheir positions which are comparable to the previous

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