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Synthetic atacamite, Cu2Cl(OH)3: A suspected spin glass behavior in low-temperature heat capacities
195
Thermochimica Acta, 88 (1585) 195-198 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
SYNTHETIC
ATACAMITE,
TEMPERATURE
Cu2Cl(OH)3:
A SUSPECTED
2 H. KAWAJI,l T. ATAKE, H. CHIHARA,l 1 Chemical Thermodynamics Laboratory 2
Science,
Osaka University,
Research
Laboratory
of
4259 Nagatsuta-cho, 3
SPIN GLASS BEHAVIOR
IN LOW-
HEAT CAPACITIES
W. MOR13 and M. KISHITA3 and Department
Toyonaka,
Engineering
Midori-ku,
Institute
of Chemistry,
Toyonaka,
Osaka 560 (Japan)
Osaka 560 Materials,
Yokohama
College
of
Chemistry,
Faculty
of
(Japan) Tokyo Institute
of Technology,
227 (Japan)
of General
Education,
Osaka University,
ABSTRACT Heat capacities of synthetic atacamite, CU~C~(OH)~, were measured in an adiabatic calorimeter between 4 and 300 K with particular attention to the relaxation phenomenon below 8 K. A suspected spin glass behavior was observed, which was compatible with previous measurements of the magnetic susceptibility.
INTRODUCTION Recent
studies of the magnetic revealed
CU~C~(OH)~.
existence
to that in spin glasses.
Thus,
susceptibilities
of a relaxation the magnetic
of synthetic
phenomenon
susceptibility
havior below 8 K; there is a peak in the susceptibility crystal
is cooled in zero external
process
following
cooled in a weak
a logarithmic
nously as thetemperature crystalline teresting
material,
is raised.
measurements
be-
at about 5.3 K when
the
Since atacamite behavior
was a very slow
if the crystal has been
field, the susceptibility
its glass-like
and precision
shows an unusual
field and the magnetization
law. On the other hand,
(~100 G) magnetic
atacamite,
below 8 K [1] similar
decreases
monoto-
is a pure, well defined
was considered
of its heat capacities
particularly
in-
have been made.
EXPERIMENTAL The specimen for magnetic solutions
used for the heat capacity
susceptibility
of CU(HCOO)~
measurements;
measurements
it was synthesized
and KCI. The powdered
by the powder X-ray diffraction.
and Cl were 58.74
(calcd. 59.51) and 16.16
nalysis.
gravimetry,
The powdered
0040-6031/85/$03.30
atomic
absorption
calorimetric
from mixed
sample thus obtained
fied as atacamite
by electro
was the same as used
The mass percentages
(16.60), respectively,
spectrophotometry,
specimen weighing
0 1985 Elsevier Science Publishers B.V.
aqueous
was identiof Cu
as determined
and gravimetric
22.460 g (0.10517 mol)
ain
vacua was loaded
into the calorimeter
for heat exchange. urements
The adiabatic
vessel with a small amount
calorimeter
was the same as will be described
Leeds & Northrup thermometers
Co.) and germanium
pressure
on the IPTS-68,
scales
used for the heat capacity elsewhere
(model CR-1000,
were used for the temperature
scales are based
helium
of helium
[2]. Platinum CryoCal
measurements.
gas thermometry
gas
meas-
(model 8164,
Inc.) resistance
Their temperature 4 He vapor
and the 1958
[2,3].
RESULTS The measured
heat capacities
Fig. 1. Existence capacity
becomes
the attainment input became
of an anomaly
between
4 and 300 K are shown in
below 8 K is evident
of atacamite
in Fig. 1; i.e. the heat
larger at lower temperatures.
of thermal rapidly
equilibrium
Furthermore, the calorimeter
longer as the temperature
to about 40 min at 5.9 K and it became certainty
within
of the measured
impractical,
heat capacity,
0
was lowered
the time needed
from 1 min above 8 K
from considerations
to wait for the complete
100
200
of un-
equilibrium
300
150
atacamita
6
-3 100 E 5 _) . op
50
0 0
0
10
for
after each energy
zoo
r/K
Fig. 1. Measured heat capacities of synthetic atacamite, equilibrium (open circles) and "instantaneous" (closed circles). The broken line shows the estimated lattice heat capacities.
197
below 5.9 K. The approach each temperature
of the thermometer
was fitted
reading
to an exponential
to a steady drift rate at
function
of the form,
(1)
T - r, = ('PO - YW)exp(-t/T),
to obtain
the time constant -T, which was then plotted
against
l/T in Fig. 2.
3
Fig. 2. Arrhenius plot of the relaxation time ? of synthetic atacamite.
/ 0
/
2
8
/
/
+ 07
0
0 /
-1
0.12
I
,
0.14
0.16
0.18
K/T The straight
line of Fig. 2 gave the activation -1 . a value of about 0.6 kJ*mol
energy of the process
governing
this relaxation
Below 5.6 K, we attempted which were obtained
by ignoring
the long time process.
are shown in Fig. 1 by filled circles. substances
is attained
ties of atacamite
the "instantaneous"
to determine
heat capacities
where T becomes
as short as 1 min. Therefore,
acteristic
they are drawn
between
heat capacilattice.
The
above 7 K,
the lattice heat capacities
5.9 K and 30 K using the Debye
200 K for 6 degrees
of freedom per formula unit,
were char-
and
line. The entropy gain due to the por-1 -1 , which account above 5.5 K is 2.4 .J*K *mol
in Fig. 1 with the broken
tion of the excess heat capacities for 40 per cent of the expected tremely
values
points
in ordinary
of the crystal
agree with the equilibrium
by smooth interpolation temperature
the "instantaneous"
to the heat capacities
"instantaneous"
estimated
These measured
Since thermal equilibration
in less than a minute,
correspond
heat capacities,
magnetic
entropy
long time to remove all the magnetic
(Rln2). It would
entropy
take
through either
an ex-
a phase
198 transition
or Schottky
from experimental heat capacity without
type of anomaly.
Therefore,
in a weak magnetic
the applied
A total thermal
ing the adiabatic the temperature
spins become
Measurements
field did not reveal any difference
frozen,
of the from those
field. analysis
was done with the crystal which had been kept at
about 5 K for more than 10 h at a constant
considered
magnetic
point of view, in the low temperatures.
condition.
recording
The result
begins
rate of energy
to decrease
as another manifestation
input while maintain-
shown in Fig. 3 is interesting when it reaches
of the relaxation
in that
about 8 K. This is
phenomenon.
Fig. 3. Temperature records in a continuous heating experiment under the adiabatic conditions. 9-
0
I IO
! 20
I
I
30
40
50
t/60s
REFERENCES 1
W. Mori and M. Kishita, Sot. Jpn. 1983, Abstract
Presented
before
47th Spring Meeting
of the Chem.
3BlO.
2
T. Atake, K. Saito and H. Chihara,
3
T. Atake and H. Chihara,
to be published
elsewhere.
Bull. Chem. Sot. Jpn. 47 (1974) 2126-2136.
Thermochimica Acta, 88 (1585) 195-198 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
SYNTHETIC
ATACAMITE,
TEMPERATURE
Cu2Cl(OH)3:
A SUSPECTED
2 H. KAWAJI,l T. ATAKE, H. CHIHARA,l 1 Chemical Thermodynamics Laboratory 2
Science,
Osaka University,
Research
Laboratory
of
4259 Nagatsuta-cho, 3
SPIN GLASS BEHAVIOR
IN LOW-
HEAT CAPACITIES
W. MOR13 and M. KISHITA3 and Department
Toyonaka,
Engineering
Midori-ku,
Institute
of Chemistry,
Toyonaka,
Osaka 560 (Japan)
Osaka 560 Materials,
Yokohama
College
of
Chemistry,
Faculty
of
(Japan) Tokyo Institute
of Technology,
227 (Japan)
of General
Education,
Osaka University,
ABSTRACT Heat capacities of synthetic atacamite, CU~C~(OH)~, were measured in an adiabatic calorimeter between 4 and 300 K with particular attention to the relaxation phenomenon below 8 K. A suspected spin glass behavior was observed, which was compatible with previous measurements of the magnetic susceptibility.
INTRODUCTION Recent
studies of the magnetic revealed
CU~C~(OH)~.
existence
to that in spin glasses.
Thus,
susceptibilities
of a relaxation the magnetic
of synthetic
phenomenon
susceptibility
havior below 8 K; there is a peak in the susceptibility crystal
is cooled in zero external
process
following
cooled in a weak
a logarithmic
nously as thetemperature crystalline teresting
material,
is raised.
measurements
be-
at about 5.3 K when
the
Since atacamite behavior
was a very slow
if the crystal has been
field, the susceptibility
its glass-like
and precision
shows an unusual
field and the magnetization
law. On the other hand,
(~100 G) magnetic
atacamite,
below 8 K [1] similar
decreases
monoto-
is a pure, well defined
was considered
of its heat capacities
particularly
in-
have been made.
EXPERIMENTAL The specimen for magnetic solutions
used for the heat capacity
susceptibility
of CU(HCOO)~
measurements;
measurements
it was synthesized
and KCI. The powdered
by the powder X-ray diffraction.
and Cl were 58.74
(calcd. 59.51) and 16.16
nalysis.
gravimetry,
The powdered
0040-6031/85/$03.30
atomic
absorption
calorimetric
from mixed
sample thus obtained
fied as atacamite
by electro
was the same as used
The mass percentages
(16.60), respectively,
spectrophotometry,
specimen weighing
0 1985 Elsevier Science Publishers B.V.
aqueous
was identiof Cu
as determined
and gravimetric
22.460 g (0.10517 mol)
ain
vacua was loaded
into the calorimeter
for heat exchange. urements
The adiabatic
vessel with a small amount
calorimeter
was the same as will be described
Leeds & Northrup thermometers
Co.) and germanium
pressure
on the IPTS-68,
scales
used for the heat capacity elsewhere
(model CR-1000,
were used for the temperature
scales are based
helium
of helium
[2]. Platinum CryoCal
measurements.
gas thermometry
gas
meas-
(model 8164,
Inc.) resistance
Their temperature 4 He vapor
and the 1958
[2,3].
RESULTS The measured
heat capacities
Fig. 1. Existence capacity
becomes
the attainment input became
of an anomaly
between
4 and 300 K are shown in
below 8 K is evident
of atacamite
in Fig. 1; i.e. the heat
larger at lower temperatures.
of thermal rapidly
equilibrium
Furthermore, the calorimeter
longer as the temperature
to about 40 min at 5.9 K and it became certainty
within
of the measured
impractical,
heat capacity,
0
was lowered
the time needed
from 1 min above 8 K
from considerations
to wait for the complete
100
200
of un-
equilibrium
300
150
atacamita
6
-3 100 E 5 _) . op
50
0 0
0
10
for
after each energy
zoo
r/K
Fig. 1. Measured heat capacities of synthetic atacamite, equilibrium (open circles) and "instantaneous" (closed circles). The broken line shows the estimated lattice heat capacities.
197
below 5.9 K. The approach each temperature
of the thermometer
was fitted
reading
to an exponential
to a steady drift rate at
function
of the form,
(1)
T - r, = ('PO - YW)exp(-t/T),
to obtain
the time constant -T, which was then plotted
against
l/T in Fig. 2.
3
Fig. 2. Arrhenius plot of the relaxation time ? of synthetic atacamite.
/ 0
/
2
8
/
/
+ 07
0
0 /
-1
0.12
I
,
0.14
0.16
0.18
K/T The straight
line of Fig. 2 gave the activation -1 . a value of about 0.6 kJ*mol
energy of the process
governing
this relaxation
Below 5.6 K, we attempted which were obtained
by ignoring
the long time process.
are shown in Fig. 1 by filled circles. substances
is attained
ties of atacamite
the "instantaneous"
to determine
heat capacities
where T becomes
as short as 1 min. Therefore,
acteristic
they are drawn
between
heat capacilattice.
The
above 7 K,
the lattice heat capacities
5.9 K and 30 K using the Debye
200 K for 6 degrees
of freedom per formula unit,
were char-
and
line. The entropy gain due to the por-1 -1 , which account above 5.5 K is 2.4 .J*K *mol
in Fig. 1 with the broken
tion of the excess heat capacities for 40 per cent of the expected tremely
values
points
in ordinary
of the crystal
agree with the equilibrium
by smooth interpolation temperature
the "instantaneous"
to the heat capacities
"instantaneous"
estimated
These measured
Since thermal equilibration
in less than a minute,
correspond
heat capacities,
magnetic
entropy
long time to remove all the magnetic
(Rln2). It would
entropy
take
through either
an ex-
a phase
198 transition
or Schottky
from experimental heat capacity without
type of anomaly.
Therefore,
in a weak magnetic
the applied
A total thermal
ing the adiabatic the temperature
spins become
Measurements
field did not reveal any difference
frozen,
of the from those
field. analysis
was done with the crystal which had been kept at
about 5 K for more than 10 h at a constant
considered
magnetic
point of view, in the low temperatures.
condition.
recording
The result
begins
rate of energy
to decrease
as another manifestation
input while maintain-
shown in Fig. 3 is interesting when it reaches
of the relaxation
in that
about 8 K. This is
phenomenon.
Fig. 3. Temperature records in a continuous heating experiment under the adiabatic conditions. 9-
0
I IO
! 20
I
I
30
40
50
t/60s
REFERENCES 1
W. Mori and M. Kishita, Sot. Jpn. 1983, Abstract
Presented
before
47th Spring Meeting
of the Chem.
3BlO.
2
T. Atake, K. Saito and H. Chihara,
3
T. Atake and H. Chihara,
to be published
elsewhere.
Bull. Chem. Sot. Jpn. 47 (1974) 2126-2136.