New Phase Transition at 155 K and Thermal Stability in KHCO3

Article abstract of DOI:10.1143/JPSJ.70.3581

The differential scanning calorimetry and thermogravimetry of KHCO₃ indicate new transformation anomalies at 155 K (T_c2), 373 K (T_d) and 459 K. The former anomaly is likely to be caused by a structural phase transition, but the latter two anomalies are related to the thermal decomposition. The chemical reaction begins at about 373 K (T_d) and reaches a complete thermal decomposition of KHCO₃ into K₂CO₃ around 459 K. The experimental results are discussed in terms of protonic intrabond and interbond jump.

Full text of DOI:10.1143/JPSJ.70.3581

Journal of the Physical Society of Japan
Vol. 70, No. 12, December, 2001, pp. 3581{3584
New Phase Transition at 155 K and Thermal Stability in KHCO3
*
1
Kwang-Sei LEE and Ill Won KIM
Department of Physics, Inje University, Kimhae 621-749, Kyungnam, Korea
1Department of Physics, University of Ulsan, Ulsan 680-749, Korea
(
Received July 27, 2001)
The diꢀerential scanning calorimetry and thermogravimetry of KHCO3 indicate new
transformation anomalies at 155 K (Tc2), 373 K (Td) and 459 K. The former anomaly is likely
to be caused by a structural phase transition, but the latter two anomalies are related to the
thermal decomposition. The chemical reaction begins at about 373 K (Td) and reaches a complete
thermal decomposition of KHCO3 into K2CO3 around 459 K. The experimental results are
discussed in terms of protonic intrabond and interbond jump.
KEYWORDS: KHCO3, phase transition, thermal decomposition, protonic defects
x1. Introduction
The crystal of KHCO is composed of K -ions and
x2. Experimental
The crystals of KHCO3 were ꢁnely crushed into
þ
3
ꢀ
(
HCO3 ) -dimers in which CO groups are bonded by a powders for diꢀerential scanning calorimetry (DSC)
2
3
double hydrogen bond. There is no hydrogen-bonded and thermogravimetry (TG) and dried at 353 K for
network through a crystal so that KHCO3 crystal is two days for removal of water molecules adsorbed at the
classiꢁed in the zero-dimensional hydrogen-bonded surface of each grain. This sample preparation is
crystal. The KHCO3 crystal undergoes a structural important for reproducible experimental results. DSC
1
{13)
phase transition at 318 K (Tc1).
involves a symmetry change from the monoclinic phase I calorimeter (DSC 2010) and TA Instruments (TGA
The phase transition and TG were performed using diꢀerential scanning
3
(
(
space group C2=m{C ) to another monoclinic phase II 2050) thermal analyzer system, respectively. Measure-
2h
space group P2 =a{C ) and is driven by the order- ments were carried out in the heating process with
disorder process of the (HCO3)2 dimers. The protons heating rates of 5 Kmin for DSC and 2 Kmin for TG
within the (HCO3)2-dimer are in disordered state with in a nitrogen atmosphere.
two equilibrium positions separated along the hydrogen
Anomalous elastic behavior in the
vicinity of 318 K (Tc1) indicated that the I{II transition Figures 1, 2 and 3 show a DSC scan of KHCO3
is of ferroelastic, but Brillouin scattering experiments contained in an aluminum pan in a nitrogen atmosphere.
5
2h
1
3
)
ꢀ1
ꢀ1
4
,5)
x3. Results
bond direction.
2
)
6
{9)
by Takasaka et al. showed that the softening of The I{II phase transition was conꢁrmed as an endother-
transverse acoustic modes is not complete and that mic peak at 317.4 K (T ). In addition, new transforma-
c1
KHCO3 undergoes an antiferrodistortive phase transi- tion anomalies were endothermically detected as a small
tion of the order-disorder type. The ferrodistortive phase peak at 155 K, a broad shoulder between 373 and 413 K
transition to the phase III (true ferroelastic phase, and a large peak at 459 K. The small endothermic peak
triclinic) occurs by an appropriate external stress both at 155 K suggests a new structural phase transition, so
in the phase I and in the phase II. Ferroelastic domains we designate 155 K as Tc2 and the low-temperature
that belong to the triclinic system are sometimes phase below Tc2 is labeled as the phase IV. The onset and
observed in the phase II, indicating phase coexistence
of monoclinic phase II and triclinic phase III at room
0)
1
temperature.
constant, thermal analysis, X-ray diꢀraction and elec-
By the measurements of the dielectric
1
1)
trical conductivity, Abdel-Kader et al.
new phase transformation around 365 K and Ali et
suggested a
1
2,13)
al.
reported anomaly near 240 K. But the experi-
mental results for new phase transformations are so poor
that the nature except a structural phase transition at
3
18 K (T ) is not yet clariꢁed. In this work, we carried
c1
out thermal study in order to search for new phase
transitions of KHCO3 and throw some light on the
nature of the transformations.
*E-mail: kslee@physics.inje.ac.kr
Fig. 1. DSC scans of KHCO3.
3
581

3582
Kwang-Sei LEE and Ill Won KIM
(Vol. 70,
Fig. 2. DSC scans of KHCO3 with enlargements of DSC signals,
revealing phase transitions.
Fig. 4. TG of KHCO3.
ðKHCO Þ ðsÞ ! 2KHCO ðsÞ
ð1Þ
ð2Þ
3
2
3
2KHCO3ðsÞ ! 2KHCO2ðsÞ þ O2ðgÞ
2KHCO3ðsÞ ! K2CO3ðsÞ þ H2OðgÞ þ CO2ðgÞ ð3Þ
where the letter s or g enclosed in parentheses denote
that the corresponding compound is in the solid state or
gas state. Reaction (1) means a transformation of the
bicarbonate dimer into two monomer ions. Continued
heating causes the monomer ion to decompose like
reactions (2) and (3). The temperature range of each
reaction was reported to be 413{493, 693{773, and 723{
1
)
8
23 K, respectively.
The present experimental results are interpreted on
the basis of above equations. But there were big
1
)
diꢀerence between Hisatsune and Adl and ours about
reactions and transformation temperatures. The ꢁrst
mass loss begins in the vicinity of 373 K and reaches a
loss of 16.0% at 441 K (inꢂection point in the thermo-
Fig. 3. DSC scans of KHCO3 with enlargements of DSC signals,
revealing onset of thermal decomposition.
oꢀset temperatures of broad shoulder were detected at gram). This is consistent with the theoretical mass of
73 and 413 K, respectively. The large endothermic peak 84.0% for the formation of KHCO2 according to the eq.
3
at 459 K means a drastic change of crystal. The (2), that is to say, the removal of one O2 molecule per
following thermogravimetry will give hints whether or molecule of the starting material KHCO3 dimer.
not the high-temperature transformations are the According to eq. (1), we can expect the reaction of the
structural phase transitions or chemical reactions.
cyclic bicarbonate dimer into two monomeric anions.
Figure 4 shows a thermogram of KHCO3 contained in This is of course possible if the hydrogen bonds are
a platinum pan. The mass loss takes place in two stages. broken and suggest a new structural phase transition
The ꢁrst mass loss begins in the vicinity of 373 K and without accompanying mass loss. But DSC did not show
reaches a loss of 16.0% at 441 K (inꢂection point in the an anomaly corresponding to monomerization due to
thermogram). The second decomposition stage accom- hydrogen-bond breaking below the onset of thermal
panied by mass loss more than 16.0% starts about 441 K. decomposition at 373 K (Td). Therefore it may be
Above 441 K, thermal decomposition is in deceleratory reasonable that in the case of the thermal decomposition
stage and the residue of ꢁnal products reaches a value of reactions of KHCO3 chemical reactions of eq. (1) and eq.
6
9.0% at 465 K. Of course, diꢀerent experimental (2) occur competitively and simultaneously. The present
conditions such as environmental atmosphere, heating thermal analysis shows that the existence of a phase
1
1)
rate, particle size, defect concentration in the crystal and transformation around 365 K is negative.
etc. can also aꢀect the thermal properties of KHCO3. In
The second decomposition stage accompanied by mass
fact, the onset temperature of mass loss strongly varied loss more than 16.0% starts about 441 K. Above 441 K,
from 368 to 383 K from sample to sample.
thermal decomposition is in a new stage and the residue
1
)
Hisatsune and Adl have studied the thermal decom- of ꢁnal products reaches a value of 69.0% in good
position reactions of KHCO3 dispersed in the KBr agreement of eq. (3) accompanied by the escapes of H2O
pressed disk by observing the changes in the infrared gas and CO2 gas and complete thermal decomposition of
spectrum of the disk with heating. They interpreted the KHCO3 into K2CO3.
thermal decomposition of KHCO3 in terms of the
following sequence of reactions:

2001)
New Phase Transition at 155 K and Thermal Stability in KHCO3
3583
hydrogen-bonded crystals has been found to vary over
the wide range being strongly dependent on the source of
x4. Discussions
1
4)
17{23)
KHCO3 is a proton conductor so that the nature of the specimen,
the reason of which may be due to the
the anomalies at 155 K (Tc2) and 373 K (Td) is likely to diꢀerent distribution of defects at the surface from
be related to the proton motions. The transition 155 K crystal to crystal. It reveals indirectly the inherent
(
motion or freezing of reorientational motion of carbonate nied by dehydration at the surface and the topochemical
Tc2) may be due to the freezing of proton tunneling tendency of thermal decomposition of crystal accompa-
2
4{26)
ions and the transformation at 373 K (T ) originates nature
d
of the high-temperature phenomenon
from the proton hopping and breaking of hydrogen around TP .
bonds. So we should consider what kind of proton defects
The very similar consideration can be extended to the
case of proton transfer in KHCO3. The protons migrate
proton intra- and change their equilibrium positions in double mini-
can be excited in KHCO3.
In the crystal family of KH2PO4,
1
5,16)
bond and interbond transfer in O{Hꢁ ꢁ ꢁO bonds is the mum potential well in various ways, for example, in
mechanism for dynamic behavior of ferroelectricity and Fig. 5.
electrical conductivity. Because of strong proton-proton
As shown in Fig. 5(a), it is possible for two protons to
interaction, such transfer is associated with thermally tunnel or hop in a concerted way, O{Hꢁ ꢁ ꢁO!Oꢁ ꢁ ꢁH{O
activated creation of H PO4 and HPO4 intrinsic along the same bond within the dimer. The eight-
3
ꢂ
‘
‘Takagi’’ defects (ionization defects), their hindered membered hydrogen-bonded ring can perform a 180 ꢂip
diꢀusion in a random-step fractal potential, and their about the Cꢁ ꢁ ꢁC vector and generate similar protonic
eventual annihilation. The orientational defects, D (two conꢁguration, but from one bond to other bond as shown
hydrogens within the Oꢁ ꢁ ꢁO bond) or L (lack of in Fig. 5(b). A proton may jump from one position to the
hydrogen), are proposed. They are thermally formed in other along the same bond. This type is an intrabond
pairs by interbond jumping between diꢀerent O{Hꢁ ꢁ ꢁO jump in which proton transfers from one bicarbonate
bonds, but migrate individually. Proton conduction group to another, giving rise to ‘‘ionization’’ defects
2ꢀ
seems to be related to the presence of defects such as H CO and CO . It is also possible for protons to jump
2
3
3
the H3PO4 and HPO4 ionization defects and/or D or L from one bond to another on the same bicarbonate group
defects. (interbond jump), giving rise to ‘‘orientational’’ defects:
There is an another kind of defects introduced recently L and D defects. Such an interbond jump leaves a
1
7)
by Lee. On heating MH2RO4-type (M¼K, Rb, Cs, Tl; hydrogen bond without a proton (L defects) and
R¼P, As) crystals, high-temperature phase transition produces a bond with protons in each of its two proton
(HTPT) has been known to occur around the onset positions (D defects). Therefore, protons can migrate
temperature T . Lee claimed that the term HTPT through the hydrogen-bonded network by concerted
p
around T in MH RO -type crystals should be replaced two-proton jumps, intrabond and interbond jumps.
p
2
4
by that onset of partial polymerization at reaction sites
17)
at the surface of solids, i.e., according to reaction:
The high-temperature anomaly of KHCO3 observed
about 373 K (Td) may be understood as due to partial
thermal decomposition at reaction sites at or near the
surface of crystal, rather than a structural phase
transition. The preliminary optical observation supports
this interpretation and spatio-temporal pattern will be
nMH2RO4ðsÞ ! MnH2RnO3nþ1ðsÞ þ ðn ꢀ 1ÞH2OðgÞ;
ð4Þ
that is,
where the letter s or g enclosed in parentheses again
denote that the corresponding compound is in the solid
state or gas state. Therefore, the intrabond and
interbond jumps may be dominant on approaching TP
of thermal decomposition of KH2PO4 crystal at the
surface and new kind defects of polymeric ions can be
generated due to hydrogen-bond breaking. The onset
temperature TP of high-temperature transformation in
Fig. 5. Two possible mechanisms of two proton transfer within the
dimer in KHCO3. (a) tunneling or jumping in a concerted way along
ꢂ
the same bond within the dimer. (b) a 180 ꢂip about the Cꢁ ꢁ ꢁC
vector from one bond to other bond.

3584
Kwang-Sei LEE and Ill Won KIM
(Vol. 70,
reported separately. Although both MH RO -type crys- Brain Korea 21 Program of Ministry of Education,
2
4
tals and KHCO3 undergo thermal decomposition at high Project No. D-0025.
temperatures, there is a big diꢀerence between MH2RO4-
type crystals and KHCO3. In MH2RO4-type crystals,
1)
2)
3)
I. C. Hisatsune and T. Adl: J. Phys. Chem. 74 (1970) 2875.
S. Hauss u¨ hl: Solid State Commun. 57 (1986) 643.
S. Kashida and K. Yamamoto: J. Solid State Chem. 86 (1990)
monomers condenses into polymers according to reaction
4) and so the onset temperature is designated as Tp. On
(
the other hand, in KHCO3 dimers are decomposed into
monomers via intermediate stage of reaction (1) and so
onset temperature is designated as Td.
1
80.
4) S. Kashida, S. Ikeda and Y. Nakai: J. Phys. Soc. Jpn. 63 (1994)
643.
M. Machida, N. Koyano and Y. Iwata: J. Kor. Phys. Soc. 32
1998) S176.
4
5
)
)
In the higher temperature region we should involve
the formation of protonic defect HCO3 molecules on
lattice cation sites by proton transfer from HCO3 ions to
another carbonate molecules, because the migration of
protonic defects requires low energy in the lower
temperature region and so defect formation requires
most of energy, assuming that the HCO ions in KHCO
(
6
S. Takasaka, Y. Tsujimi and T. Yagi: J. Kor. Phys. Soc. 29 (1996)
S444.
7) S. Takasaka, Y. Tsujimi and T. Yagi: Phys. Rev. B 56 (1997)
0715.
1
8
)
S. Takasaka, Y. Tsujimi and T. Yagi: J. Kor. Phys. Soc. 32 (1998)
S565.
S. Takasaka, Y. Tsujimi and T. Yagi: Ferroelectrics 219 (1998)
3
3
9
)
is in a state of torsional oscillation, from which it changes
to a state of free rotation in the vicinity of 373 K. This
free rotation might cause the generation of a large
number of protonic defects giving rise to an increase in
electrical conductivity. In order to test which kinds of
defects contribute to the electrical conductivity, the
detailed experimental study is underway and will be
reported elsewhere.
4
10) Y. L. Grand, D. Rouede, J. Wienold and J. Glinnemann: J. Phys.
7.
Soc. Jpn. 67 (1998) 1451.
1) M. M. Abdel-Kader, M. Fadly, M. A. Taleb, K. Eldehamy and
A. I. Ali: Phys. Status Solidi A 142 (1994) 69.
1
1
2) A. I. Ali, B. S. Kim and I. Yu: J. Kor. Phys. Soc. 35 (1999) S1419.
3) A. I. Ali: Ph. D. Thesis, Seoul National University, 2001.
14) Ph. Colomban and A. Novak: Proton Conductors, ed. Ph.
1
Colomban (Cambridge University Press, Cambridge, 1992) p. 80.
5) V. H. Schmidt: J. Mol. Struct. 177 (1988) 257; Ferroelectrics 78
1988) 207.
1
(
x5. Conclusions
We found the new transformation anomalies at 155 K
1
6) Ph. Colomban and A. Novak: Anhydrous Materials: Oxonium
Perchlorate, Acid Phosphates, Arsenates, Sulphates and Selenates
in Proton Conductors, ed. Ph. Colomban (Cambridge University
Press, Cambridge, 1992) Chaps. 10 and 11.
(
Tc2), 373 K (Td) and 459 K in KHCO3. The low-
temperature transformation is likely to be due to freezing
of proton motions, while the high-temperature transfor-
mation begins at temperature 373 K (Td) well below
1
1
7) K.-S. Lee: J. Phys. Chem. Solids 57 (1996) 333.
8) J.-H. Park, K.-S. Lee, J.-B. Kim and J.-N. Kim: J. Phys.:
Condens. Matter 8 (1996) 5491; ibid. 9 (1997) 9457.
19) J.-H. Park, K.-S. Lee and J.-N. Kim: J. Kor. Phys. Soc. 32 (1998)
4
ture 373 K (T ) which is interpreted as an onset of
59 K. The bulk mass of KHCO decreases at tempera-
3
d
Suppl. S1149.
0) J.-H. Park, K.-S. Lee and J.-N. Kim: J. Phys.: Condens. Matter
0 (1998) 9593.
2
2
2
partial thermal decomposition, i.e., the chemical reaction
begins at about 373 K (Td) and reaches a complete
thermal decomposition of KHCO3 into K2CO3 around
1
1) K.-S. Lee, J.-H. Park, K.-B. Kim, J.-B. Kim and J.-N. Kim: J.
Phys. Soc. Jpn. 66 (1997) 1268.
2) J.-L. Kim and K.-S. Lee: J. Phys. Soc. Jpn. 65 (1996) 2664.
4
59 K. The ꢁrst stage of two high-temperature transfor-
mations is accompanied by the escape of O2, and the
second stage is related with the loss of H2O and CO2.
These phenomena are discussed in terms of proton
migration through the hydrogen-bonded network by
concerted two-proton jumps, intrabond and interbond
jumps.
23) K.-S. Lee, J.-L. Kim, H.-T. Jeong and S.-Y. Jeong: J. Kor. Phys.
Soc. 29 (1996) Suppl. S424.
2
4) W. P. Gomes and W. Dekeyser: Factors Inꢀuencing the Reactiv-
ity of Solids, ed. N. B. Hannay (Plenum Press, New York, 1976)
Treatise on Solid State Chemistry, Vol. 4 (Reactivity of Solids),
pp. 61{113.
25) F. C. Tompkins: Decomposition Reactions, ed. by N. B. Hannay
Plenum Press, New York, 1976) Treatise on Solid State
Chemistry, Vol. 4 (Reactivity of Solids), pp. 193{231.
(
Acknowledgements
2
6) M. E. Brown: Introduction to Thermal Analysis: Techniques and
Applications (Chapman and Hall, New York, 1988) Chaps. 2 and
This work was supported by grant No. 2001-1-11400-
12-1 from the Basic Research Program of the Korea
0
Science and Engineering Foundation and in part by the
1
3.