American Mineralogist, Volume 72, pages 739-747, 1987
Ionic conductivityof quartz:DC time dependence
and
transition in charge carriers
A. K. KnoNENBERG
Geophysics
Department,TexasA&M University,CollegeStation,Texas77843,U.S.A.
S. H. KRsv
U.S. Geological Survey, 345 Middlefield Road, M.S. 977, Menlo Park, California 94025, U.S.A.
Commemorativephotograph of Jacquesand Pierre
Curie (left and right, respectively)in 1878.Courtesyof
S. Leher, Centre de RessourcesHistoriques, ESPCI,
paris.
Arsrn-q.cr
The time dependenceof DC electrical conductivity in the c-axis direction of quartz can
be accounted for by a transition in charge carriers from interstitial alkali impurities to
interstitial H. The diffusive transport rates of Li, Na, and K are rapid parallel to c and
have been shown to be responsiblefor the highly anisotropic electrical conductivity measured at short times. With increasingtime, however, conductivities parallel to c decrease
progressivelyto values that are roughly equal to those measuredperpendicularto c. Comparison of these ultimate, nearly isotropic conductivities with those derived from recent
measurementsof H diffusion parallel and perpendicular to c suggeststhat H interstitials
are the principal charge carriers at long times. The transient decreasein conductivities
parallel to c is interpreted to result from depletion of initial alkali impurities, whereasthe
steady-stateconductivities measuredat long times may be sustainedby the steady supply
of H by the dissociation of atmospheric water vapor. The mobility of H along the c axis
is anomalously low and at variance with the trend of increasingmobility with decreasing
ionic radius exhibited by Cs, Rb, K, Na, and Li. Although the elastic lattice distortions
required for H transport are insignificant in comparison with those required by the larger
alkali impurities, the strong associationof H interstitials with Al substitutions for Si may
be responsiblefor the relatively low H mobilities.
INrnonucrroN
Just 100 yearsago,JacquesCurie (1886, 1889)and E.
Warburg and F. Tegetmeier(1887, 1888)made the first
measurementsof the direct current ionic conductivity in
q'rartz. In theseearliest studiesof the electricalproperties
of minerals, Curie and Warburg and Tegetmeier made
key observationsthat have endured a century ofresearch
on quartz conductivities, and they proposedmechanisms
of charge transport that resemblecurent models. Curie
discoveredthat the DC conductivity of quartz in the c-axis
direction depends upon time (the current decaying ex0003404x/87/0708-0739S02.00
ponentially with time) and proposedan electrolytic model of chargetransport involving molecular water and dissolved salts in the c-axis channels. Likewise, Warburg
and Tegetmeierrecognizedthe time dependenceof conductivity in quartz and suggesteda charge-transport
mechanism involving the migration of Na ions initially
present as impurities in the quartz structure. Since these
pioneering studies, measurements of conductivity in
quartz have been extended to temperatures of up to
1200'C and DC excitation times rangingfrom 0.5 to 106s
(as well as AC frequenciesfrom 20 to l0? Hz), both for
739
740
KRONENBERG AND KIRBY: IONIC CONDUCTIVITY OF QUARTZ
DC - Electrical Conductlvlty
BrazilianOuartz llc (Wenden,
I
Fig. l. Direct currentconductivitiesmeasuredparallelto c
asa functionof time (afterWenden,1957).
natural and synthetic crystals in the c-axis direction and
perpendicular to it. Alkali impurities, as originally proposed, are now known to be important charge carriers
accountingfor DC conductivities (and AC conductivities)
measuredat short times parallel to c.
On the centennial of the original experiments of electrical properties of quartz, we commemorate these early
experimental mineralogists and take this opportunity to
compare the DC conductivities of quartz measured at
long times with recent results obtained for H diffusion.
On this basiswe proposeda model for steady-statecharge
transport involving interstitial H. Although the long-time
conductivity ofquartz is unlikely to control the bulk electrical propertiesofrocks in which intergranular fluids carry much of the current, determination of its mechanisms
should help to evaluate the defect chemistry of quartz
and its effectson such diverse phenomena as coloration
(Cohen, 1960; Kreft, 1975; Weil, 1975; Halliburton et
al., 1981),hydrolyticweakening(Griggs
and Blacic,1965;
Hirsch, l98l; Hobbs, l98l), and Si and oxygendiffusion
(Dennis, 1984; Giletti and Yund, l98a) by placing constraints on defect mobilities and internal charge transport.
Rybach and Laves, 1967; Frischat, 1969, 1970a, 1970b),
suggestingthat they are the principal charge carriers in
the c-axis direction. With increasingtime, however, DC
conductivities measuredparallel to c decreaseby several
orders of magnitudeapproachingthose measuredperpendicular to c. CorrespondingAC conductivities measured
parallel to c do not show time-dependent behavior but
are affectedby prior application of DC fields.
In a study explicitly designedto investigate the time
dependenceof c-axis conductivities, Wenden (1957)
measured DC conductivities (Fig. l) for times of up to
5 x 106s (1400 h) and showed that much of the scatter
in reported DC conductivities parallel to c (Fig. 2,A)could
be explained by variations in time of current passage.DC
conductivities measured parallel to c exhibit an initial
transient decreaseleveling offwith time to nearly steadystate values. Accompanying this transition, the apparent
activation energies of transient and steady-statec-axis
conductivities differ, increasingfrom 100 to 165 kJlmol
(Wenden, 1957), respectively.Conductivitiesmeasured
perpendicularto c show a far smaller transient response,
and the scatterin reported DC conductivities perpendicular to c is correspondingJymuch smaller (Fig. 2B). Conductivities measured perpendicular to c are essentially
the sameas the steady-statec-axis conductivities with an
apparentactivation energyof 180 kJlmol (Rochow, 1938;
Sarzhevskii,1952).
Interstitial alkali impurities have repeatedlybeen shown
to be the principal charge carriers controlling short-time
c-axis conductivities (Table l); the transient decay of
c-axis conductivities have therefore been interpreted to
result from the depletion of alkalis. The mechanisms of
chargetransport at long DC times and those acting perpendicular to c have received less attention, and charge
carriersproposedinclude electronic as well as ionic point
defects.In this paper, we proposethat intrinsic electronic
conductivities have never been measured and that the
isotropic long-time DC conductivities are controlled by
the diffusion of interstitial H.
DrnrusroN or H
The diffusion ofH in quartz (Fig. 3) has been studied
by measuringthe rates of H uptake, H-D exchange(Kats,
I 962; Kronenberg et al., I 986), and tritium uptake (Shaffer et al., 1974). At high temperature (7 > 620'C), H
Er,Bcrnrcar, coNDucrrvrry oF euARTZ
diffusion is essentiallyisotropic with relatively large acThe electricalconductivity of quartz measuredat short tivation energiesof 175 kJ/mol (Kats, 1962) to 200-210
DC times, or under alternating currents, is extremely an- kJ/mol (Kronenberg et al., 1986). Diffusion of H at temisotropic with conductivities parallel to c exceedingthose peraturesbelow 620"C exhibits a smaller activation enmeasured perpendicular to c by more than 103 (Joffe, ergy of 80 kJlmol (Kats, 1962), associatedwith a change
1928; Rochow, 1938; Sarzhevskii,1952; Strausset al., in H speciation(Kats, 1962;Aines and Rossman,1984).
1956; Wenden, 1957;,Glushkova and Firsova, 1968). Interstitial H defects at high temperatures are strongly
Correspondingto this anisotropy, the diffusive transport associatedwith Al substitutions for Si and lead to a H
rates of alkali impurities occupying interstitial sitesalong solubility limit given by the local charge neutrality conthe c-axis channelshave been shown to be rapid (Harris dition [H;] : [Al!,] (Kats, 1962;Kronenberget al., 1986)
and Waring, 1937;Vogel and Gibson, 1950;Gibson and and the Al concentration (which may range from 60 to
Vogel, 1950; Verhoogen, 1952; Stuart, 1955; Wenden, 300 atoms Al per 106atoms Si). At low temperatures,
1957;Milne and Gibbs, 1964;Snow and Gibbs, 1964; however, H interstitials are not associatedwith Al centers
't
4l
KRONENBERG AND KIRBY: IONIC CONDUCTIVITY OF QUARTZ
I
c
E
c
o
b
(JO
8
On
O
8
o^
t/r
P
YO
5
o
tlr
Fig. 2. Collected conductivity data as a function of temperature. (A) Arrhenius plot of conductivities measuredparallel to c
showscatteroverseveralordersofmagnitude(Exner,1901;Joffe,1928;Verhoogen,1952;Bottom,1953;King,1955,1956;Strau
et al., 1956;Wenden, 1957).Wenden (1957) showedthat the wide spreadin reportedconductivitiescould be explainedby the
decreasein conductivity with time. (B) Arrhenius plot of conductivities measuredperpendicularro c (Joffe, 1928;Sarzhevskii, 1952;
Rochow. 1938:Strausset al.. 1956).
to any great extent (Kats, 1962).This transition in defect
chemistry, though suggestivelynear the transition between high (B) and low (a) qtrartz, does not appear to
correspond exactly to the a-B transition temperature
(573"C)at the near-ambientpressures(0.1 to 2.5 MPa)
employed by Kats (1962).
Shaffer et al. (1974) measured H diffusion within the
high temperature range @t f : 720-850'C), but their
experiments were done at rather low pressures(P"ro =
0.06 MPa), and their reported diffusivities are orders of
magnitudesmaller than those of Kats (1962, measured
al PH2o: 2.5 MPa) and Kronenberget al. (1986, measured at Pnro: 890 MPa) with activation energies(90110 kJlmol) comparableto that reported by Kats (1962)
for lower temperatures.We speculatethat this discrepancy is due to a change in H speciation at low water
pressures.
INnrnnno coNDUCTrvrrIES
Kats (1962) first proposed that H may be an important
chargecarrier parallel to c on the basis of comparisonsof
his diffusion results with DC conductivities measuredat
long times (Table l). Along similar lines, White (1971)
proposed that hydroxyl difusion may be an important
conduction mechanism parallel to c; however, measure-
ments of oxygendiffusion under hydrothermal conditions
(Dennis, 1984;Giletti and Yund, 1984)suggestthat hydroxyl mobilities are much smaller than those of interstitial H. More recent studiesofelectrolytic sweeping(Lo-
1. Proposed
TABLE
chargecarriersin quartz
Point defect
Lii
Nai
K;
Rb;
csi
H;
oHi
e'orh
( a t t i m e s> 5 x 1 0 s s )
IC
e'
ionic(f > 300'C)
e'(r < 300'C)
ionic(shorttimes)
e' or h (longtimes)
References*
2 , 4 , 7 , 8 , 1 11, 3 , 1 4
1 , 2 , 5 , 7 , 91, 1 ,1 3 ,1 4
7,11
'11
'lI
10,14
12
9
o
I
. 1, Warburgand Tegetmeier,1888; 2, Harris and Waring,
1937; 3, Rochow,1938; 4, Gibsonand Vogel,1950; 5, Vogel
a n d G i b s o n1
, 9 5 0 ;6 , S a r z h e v s k i1i ,9 5 2 ; 7 ,V e r h o o g e n1, 9 5 2 ;
, 9 5 7 ;1 0 , K a t s ,1 9 6 2 ;1 1 ,W h i t e ,
8 , S t u a r t ,1 9 5 5 ;9 , W e n d e n 1
1 9 7 0 ; 1 2 ,W h i t e ,1 9 7 1 ; 1 3 , J a i n a n d N o w i c k ,1 9 8 2 a ,1 9 8 2 b ;
1 4 , L o p e ze t a l . , 1 9 8 6 .
KRONENBERGAND KIRBY: IONIC CONDUCTIVITY OF QUARTZ
742
TneLe 2. Activation energies for c-axis diffusion
ro-9
exchange llc
Point defect
F(kJ/mol)
References'
exchang9 Ic
o
E
Li;
60
o
c
17s (r > 620'c)
200-210
80 (r < 620'c)
90-110
72-90
r v
H'D
exchange
llc
H-D €xchano€ llc
Nai
KA
T uptake llc
K;
6000c
1tf
500ec
90-105
100
102
84
88
I
4
6
'I
3
7
2
e
5
o
133
117
J
Rbi
125
7
csi
138
7
7
. 1 , G i b s o na n d V o g e l ,1 9 5 0 ;2 , V o g e la n d G i b s o n ,
1 9 5 0 ; 3 , V e r h o o g e n1, 9 5 2 ; 4 , K a t s ,1 9 6 2 ; 5 , R y b a c h
and Laves,1967; 6, Frischat,1969, 1970a,1970bi 7,
White,1970; 8, Shafferel al., 1974i 9, Kronenberget
al.,1986.
Fig. 3. Arrheniusplot of collecteddiffusiondata for H in
quartz.H diffusionis nearlyisotropicwith relativelylargeacti(E*: 175kJlmol,Kats,1962;E*:200-2IO
vationenergies
kJ/mol,Kronenberg
(7 > 620"C)
etal., 1986)at hightemperatures
anda smalleractivationenergy(E* : 80 kJ/mol,Kats, 1962)at
(T < 620'C).Thediffusivitiesreportedby Shaflowtemperatures
fer et al. (1974)areordersof magnitudesmallerthan thoseof
ities due to Na and H migration form an envelopearound
Kats(1962)andKronenberg
et al. (1986).
conductivities measuredparallel to c. For directions perpendicular to c, the mobilities of H and Na are rather
pez et al., 1986) and measurementsof H diffusion both similar, and either defect may account for the observed
parallel and perpendicular to c (Kronenberg et al., 1986) conductivities. The time dependenceof conductivities
have confirmed the original results of Kats (1962) and parallel to c can therefore be explained by a transition in
have shown that the diffusion of H in quartz is nearly charge carriers from initial alkali interstitials to interstiisotropic. Ionic conduction in quartz due to H diffusion tial H (Fig. 5). The inferred conductivities due to the
Rybach
may therefore be expectedto be isotropic.
diffusion of Li, N4 K, and Cs (Verhoogen, 19521,
Given the identification ofH defectsas chargedinter- and Laves, 1967; Frischat, 1969, 1970a, 1970b;White,
stitials with concentrations (given by the local charge 1970) compare favorably with the initial conductivities
neutrality condition [H;] : [Al!j) of the order of 100 ppm measuredby Wenden (1957); the inferred conductivities
(atoms H per 106atoms Si), the expectedconductivities due to H diffusion (Kats, 1962;'Kronenberg et al., 1986)
due to H diffusion can be determined using the relation- compare more favorably with the ultimate, steady-state
ship between ionic conductivity and tracer diffusion, as conductivities. H, unlike the initial alkali impurities, can
be supplied at a steadyrate by dissociation of atmospherderived from the Nernst-Einstein relationship:
ic water vapor at the anode, giving rise to steady-state
(l)
o: cslD/kT,
conductivities. Transient conductivities at intermediate
where c, is the concentration of charged interstitial de- times may thus be modeled, though we have not explicfects, 4, is the chargeofthese interstitial defects,D is the itly done so, by solving for chargeddefect mobilities cortracer difrrsion coefficient,k is Boltzmann's constant,and responding to simultaneousgradientsin their concentraZ is the temperature in kelvins (Shewmon, 1963). Like- tions and in the electrical potential.
wise, we can estimate the conductivities due to the difH aNn
CoNrp.q.nrsoNoF TNTERSTTTTAL
fusion of alkali interstitials assumingtheir initial concenMOBILITIES
ALKALI
(again
trations are also limited by the initial Al content
we use 100 ppm). Although the alkalis may be presentat
Although the transition from alkali to H chargecarriers
theseconcentrationsinitially, they are expectedto be de- appearsto explain the behavior of quartz c-axis conducpleted with time under a DC field.
tivities, the low rates of H diffusion relative to those of
Making use of the above relation and tracer-difusion the alkalis requires discussion.Becausealkali and H inresults for Na; (Frischat, 1969, 1970a, 1970b) and H; terstitials have the same effective charge, their relative
(Kats, 1962;,Shafferet al., 1974; Kronenberget al., 1986) mobilities might be expectedto correlate inversely with
we compare inferred conductivities (Fig. a) with the col- the lattice distortions required for their migration. Aclected measuredconductivities. The inferred conductiv- cordingly, the rates ofdiffusion for the alkalis along the c
743
KRONENBERG AND KIRBY: IONIC CONDUCTIVITY OF QUARTZ
Quortz
Quorlz
(Kronenberg
'r e t a l . . 1 9 8 6)
(J(J
oo
a)O
-o
O
o
t/ r
o
sr9
xo
(J
o
-
tr)
l/T
Fig. 4. Comparison of inferred conductivities based on H (Kats, 1962; Shafferet al., 1974; Kronenberg et al., 1986) and Na
(Frischat, 1970b) diffusivities with the collected conductivity data (shown in Fig. 2) parallel (A) and perpendicular(B) to c.
axis of quartz exhibit a systematicvariation of increasing
mobility with decreasingionic radius (Fig. 6). When comparedwith this trend, however,the diftrsion of interstitial
H is anomalously slow.
On the basis of the high-temperatureassociationof H
with Al impurities, we suggestthat the anomalously low
mobilities of H result from a large associationenthalpy
that must be overcome for diffusion. Both alkali and H
interstitials have been shown to act as charge-compensatingdefectsfor Al substitutionsfor Si (Bambauer,1961;
Bambaueret al., 1962, 1963; Kats, 1962; Stevelsand
Volger, 1962; Snow and Gibbs, 1964; King and Sander,
1972;Park and Nowick, 1974; Markes and Halliburton,
1979; Weil, 1975; Hallibufron et al., l98l; Jain and
Nowick, 1982a, 1982b).However, the alkalis, residing in
the c-axis channels(Fig. 7) form an essentiallyionic bond
with the Al center, whereasH is expectedto bond to a
bridging oxygen and requires much larger energiesto remove (Sykesand Weil, 1970; Nuttall and Weil, l98l).
Correspondingto this additional bonding, the activation
energiesfor H difusion in the c-axis direction ofquartz
(at temperaturesgreater than 620"C) appear to be larger
than those determined for alkali diff.rsion (Table 2). Thus,
once removed from an Al site, H is expectedto have a
greater mobility than those of the larger alkali interstitials; the largeAl-H pair enthalpy must first be overcome,
however, to form an unassociated(or free) H interstitial.
Unlike the larger alkalis, free H interstitials are not restricted to the c-axis channelsand may migrate perpendicular to c at the same rates as those parallel to c. At
low temperatures (Z < 620"C), H interstitials occur at
numerous sites unrelated to Al impurities (Kats, 1962),
and here the activation energiesare more comparable
with those for alkali diffusion.
Moonr, oF H DrFFUsroN
We propose a model for H diffusion, which in some
respectsresemblesthat of Jain and Nowick (1982a) for
interstitial alkalis, wherein we distinguish between H interstitials that are associatedwith Allt and H that is not.
744
KRONENBERG AND KIRBY: IONIC CONDUCTMTY
OF QUARTZ
(Ffischat, | 970b)
Na
I
Li
'
(White,l970)
DC - Electrical
Conductivity
B r a z i l i aQ
n u a r t z l l c ( W e n d e n1,9 5 7 )
T - 5000c
I
:
E
Li.(Verhoogen,1952)
I
Nal(Rybach&Laves,
E
I
E
o
b
-
C s ' ( W h i t e ,l 9 7 O )
to-6
oH | (wt'itr. t gz t)
I
I
Na'(Verhoogen,1952)
H,(Kats,l962)
K . ( V e r h o o g e n| ,9 5 2 )
HI (Kronenberg
I et at., 1986)
Shaffer et al.. | 974)
4xto4
TtME (s)
zxto4
6xto4
Sxld
Fig. 5. Inferred c-axis conductivitiesbasedon alkali (Li, Verhoogen,1952,and White, 1970;Na, Verhoogen,1952, Rybach
andLaves,lg6T,andFrischat,1970b;K,Verhoogen,1952;CS,White,1970)andH(Kats, 1962;Shafferetal.,l914;Kronenberg
et al., 1986)difusion at (and, in some cases,extrapolatedto) 7: 500'C. The inferred hydroxyl conductivity ofWhite (1971) is
also shown. The inferred alkali conductivities compare favorably with measuredconductivities at short times (fine lines, as shown
in Fig. 1, taken from Wenden, 1957, for T : 496 and 536"C), whereasthe inferred H conductivities match more closely the longtime conductivities.
10+
Alkali lmpurity Diffusion
in Quartz
T : 5O0oC
197ob)
llc (white, 197o)
o
. ( R y b a c h& L a v e s ,
o
llc
doH
(White, 1971)
1 0'13
,*,* {,ui;:?3n""'
19 7 0 b )
et al.. 1974)
HLiNaKRbCS
Increasing lonic Radius *
500'C (Verhoogen, 1952;
Fig. 6. H and alkali diffusivities as a function ofincreasing ionic radius at (and extrapolated to) 7:
Kats, 1962; Rybach and Laves, 1967; Frischat, 1970b; White, 1970, l97l; Shatrer et al.,1974; Kronenberg et al., 1986).
KRONENBERG AND KIRBY: IONIC CONDUCTIVITY OF QUARTZ
745
A
H;- Ars; ASSOCTATTON
H i S l t e I ( K a r s, 1 9 6 2)
o
H - Af dlst. = 2.1OA
B
Hi' Site 2 ( Kats , 1962 )
o
H - Al dist. = 1.06 A
c
( Ark);-Als;
ASSOCTAflON
o
Alk - Al dist. = 2.50 A
Fig. 7. Interstitial H and alkali sites associatedwith Al substitutionals. Al-associatedH sites I and 2 (A and B, respectively)
proposed by Kats (1962) for quartz at high temperatures (H-Al distances of 2.10 and 1.06 A, respectively).(C) Al-associated
interstitial alkalis occupy the center of the c-axis channels(H-Al distance of 2.50 A).
Kats (1962) effectively demonstrated that H interstitials
at high temperatures(T > 620"C)are associatedwith Al
defects but that a large number of other interstitial H
sites,which are unrelated to Al centers,exist at low temperatures (T < 620'C). Given that Al is essentiallyimmobile, the diffusion of H at high temperaturesrequires
the dissociation of Al-H pairs to form free H; followed
by transport to neighboring Al!, sites. At low temperatures, a large fraction of H interstitials is not associated
with Al substitutionals (Kats, 1962; Aines and Rossman,
1984),and their mobilities do not dependon H-Al dissociation. With this interpretation, the changein activation energyof H diffusion at low and at high temperatures
may representthe enthalpy required to remove H interstitials from Al sites.
Il at high temperatures,H diffusion occursby the motion of H; from one Al!, site to another, its diffusion coefficient D can be expressed(Shewmon,1963)as
D:
ka2Caw,
(2)
where a is the mean Al-Al spacing (-7 nm for an Al
concentration of 100 ppm), Cd is the concentration of
uncompensatedAl sites, w is the probability that a free
H; will jump to a neighboringAl!, site, and k is a geometric
factor. At equilibrium, the concentrationsof both mobile
H; and uncompensatedAllt are given by
Co : [exp A,Sd/R)]lexp(-AHo/RT),
(3)
where ASoand A11orepresentthe changesin entropy and
enthalpy, respectively,of the crystal for eachH; removed
from an Al!, site. Similarly, the probability that a free
H; will jump to a particular Al!, site is given by
w:
z[exp(AS-/R)][exp(-A]1-lR?")1,
(4)
where AS. and A.Fl- are the entropy and enthalpy, respectively, of the H mobility and y is the frequency with
which H; defectsmidway betweentwo Al siteswill move
to the new site. Combining Equations2,3, and 4,
D:
kva2lexp(A,Sd+ AS-yR)l
lexp(-(al/" + AH^)/RT)].
(5)
The empirically derived temperature dependenceis thus
interpreted to representthe sum ofenthalpies for H dissociation from one AI site and for mieration to a new AI
site.
746
KRONENBERG AND KIRBY: IONIC CONDUCTIVITY OF QUARTZ
If, at low temperatures,H is presentas interstitials that
are not associatedwith Al, its diffusion coemcient(Shewmon, 1963)is independentofconcentration:
p:
ya2w,
(6)
where a is the jump distance, w is the probability that a
particular interstitial will jump, and 7 is a geometric factor. Here, again, the probability may be expressedaccording to Equation 4, where ,, representsthe jump frequency and AS- and ArI-, respectively, represent the
entropy and enthalpy of H; movement, so that Equation
6 can be written
p : Tva2lexs(AS-/R)llexp(-AH^/RT)1.
(7)
If we chooseto define all of the parametersin Equation
7 for the same distance as the averageAI-AI spacing of
the crystal, we can compare the high- and low-temperature relations and interpret the measuredchangein activation energies(from 175 to 80 kJlmol = 100 kJ/mol,
Kats, 1962) to representthe Al-H pair enthalpy. The activation energyfor H diffusion (of 80 kJlmol, Kats, I 962)
measuredat low temperaturesis thus interpreted to represent the enthalpy of H motion over the mean Al-Al
spaclng.
CoNcr-usIoNs
Comparisons of DC conductivities of quartz with diffusional transport rates ofalkali interstitials and interstitial H lead to the following conclusions:
1. Anisotropic conductivities measured at short DC
times (or under AC fields)parallel to c comparefavorably
with those inferred from the diffusion of interstitial alkali
impurities.
2. Isotropic conductivities measuredat long DC times
compare favorably with those inferred from the diffusion
of interstitial H.
3. The time dependenceof DC conductivities parallel
to c is due to the depletion of initial alkali impurities and
a transition in charge carriers to interstitial H. At short
times, conductivities measured parallel to c are controlled by alkali mobilities, whereasconductivities measured perpendicular to c may be controlled by either alkali or H mobilities. At long times, the nearly isotropic
conductivities are controlled by the mobility of H interstitials in all directions. Apparently, intrinsic, electronic
conductivities have not, as yet, been measured.
4. H diffusion parallel to c is slow relative to that of
larger alkali interstitials owing to the strong association
of H;wirh Al!,.
5. The changein activation energy for H diffusion at
high and at low temperaturesmay representthe enthalpy
required to dissociate H interstitials from Al substitutions for Si.
AcrNowr-sncMENTs
We would like to thank D. Lockner for helpful discussionsand for his
thoughtful review of our manuscript. We also extend thanks to R. A.
Yund for discussionsthat helped clarify our thoughts.Many thanks go ro
S. Leher and the Centrede RessourcesHistoriques, ESPCI,Parisfor kindly providing the photographofJacques and Pierre Curie.
RnrBnrNcns
Aines, R.D, and Rossman,G.R. (1984)Water in minerals?A peak in
the infrared Journal of GeophysicalResearch,89, 4059-407|
und 7-Farbzentrenin
Bambauer,von H.U. (1961)Spurenelementgehalte
Quarzen aus Zerrkliiftenden der SchweizerAlpen. SchweizerischeMineralogischeund PetrographischeMitteilungen, 41, 335-369.
Bambauer,von. H.U, Brunner,G.O., and Laves,F. (1962)WasserstoffGehalte in Quarzenaus Zerrkliiften der SchweizerAlpen und die Deutung ihrer regionalenAbhiingigkeit SchweizerischeMineralogischeund
PetrographischeMitteilungen, 42, 221-236.
(1963) Merkmale des OH-Spektrums alpiner Quarze(3 p-Gebiet).
SchweizerischeMineralogischeund PetrographischeMitteilungen, 43,
259-268
Bottom, V.E. (1953)Final report; SignalCorps contract.In Wenden, 1957,
below.
Cohen, A J. (1960) Substitutional and interstitial aluminum impurity in
quartz, structure and color center interrelationships. Intemational
Journal of the Physicsand Chemistry of Solids, 13, 321-325.
Curie,J (1886)In Wenden, 1957,below
-(1889)
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M,qNuscrrpr
MeNuscnrpr
REcETVEDOcrossn 13, 1986
AccEprED Mencn 23. 1987