1H and 39K nuclear magnetic resonance relaxation study in a KHSO4 single crystal

Full text of DOI:10.1143/JPSJ.72.1308

J. Phys. Soc. Jpn.
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Journal of the Physical Society of Japan
Vol. 72, No. 5, May, 2003, pp. 1308–1309
#2003 The Physical Society of Japan
SHORT NOTES
method were investigated using a pulse NMR spectrometer.
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1
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H and K Nuclear Magnetic Resonance
Relaxation Study in a KHSO Single Crystal
39
The relaxation times of the H and the K nuclei in a
KHSO4 single crystal are new observations.
4
Single crystals of KHSO4 were grown at room tempera-
ture by using slow evaporation of an aqueous solution
containing a stoichiomeric proportion of K2SO4 and H2SO4.
The crystals with hexagonal shapes were colorless and
transparent and had good optical quality. The NMR signals
ꢀ
1
Ae Ran LIM , Hee Won SHIN and Dong Young JEONG
Department of Physics, Jeonju University, Jeonju 560-759, Korea
1Institute of Quantum Information Processing and Systems,
The University of Seoul, Seoul 130-743, Korea
1
39
of H and K in the KHSO crystal were measured using the
4
(
Received December 2, 2002)
Bruker MSL 200 FT NMR and the Bruker DSX 400 FT
NMR spectrometers, respectively, at the Korea Basic
Science Institute.
KEYWORDS: crystal growth, crystal structure, nuclear magnetic
resonance (NMR)
DOI: 10.1143/JPSJ.72.1308
1
The H spin–lattice relaxation time was measured in the
Proton conducting solids are of potential interest for fuel temperature range from 140 K to 400 K at a frequency of
cells, steam electrolysis, and as sensors. Proton conduction 200 MHz. The spin–lattice relaxation time, T , was mea-
1
ꢂ
ꢂ
occurs in several types of materials including many hydro- sured by applying a pulse sequence of 180 –t–90 . The
1
ꢂ
gen-bonded systems. In some ferroelectric and ferroelastic nuclear magnetization SðtÞ of H at time t after the 180
hydrogen-bonded crystals the superionic conductivity was pulse was determined from the inversion recovery sequence
discovered: MHSO (M = K, Rb, Cs, NH ) exhibit high following the pulse. The recovery traces of the magnetiza-
4
4
proton conductivity in their high temperature phases. The tion of the crystals were measured at several different
1
hydrogen sulfate family, MHSO4 has received much atten- temperatures. The recovery traces of H show a single
1
)
tion owing to its interesting properties. The most interest- exponential function. The temperature dependence of T for
1
1
ing group in the crystal structures of this series is the HSO4
ion, which is usually distorted and arranged, in a tetrahedral
H in the single crystal is shown in Fig. 1. In the case of the
H nucleus, the spin–lattice relaxation time is long with
1
symmetry. Potassium hydrogen sulfate, KHSO , is a T ¼ 382 s at room temperature. The variation of the
4
1
ꢁ
1
member of the alkali acid sulfate family interesting because relaxation rate, T , with temperature exhibits a minimum.
1
2
)
1
of its ferroelectric behavior. Until now, the phase transition As the temperature is increased, the H relaxation rate
temperature in the KHSO4 crystal has not been exactly slowly decreases, and then begins to increase, passing
3
–5)
ꢁ1
established.
The structure of a KHSO4 single crystal is orthorhombic temperature range has a positive parabolic shape with a
through a minimum at 210 K. The curve of T1 in this
1
5
with space group Pbca (D ) and with sixteen molecules per minimum near 210 K. This result is not consistent with the
2
h
ꢀ
1
ꢁ1
unit cell. The unit cell parameters are a ¼ 8:4030 A, trend of H in the hydrogen sulfate family: the shape of T
1
6
)
þ
1
ꢀ
ꢀ
b ¼ 9:799 A, and c ¼ 18:945 A. All the 16 K and 16 for H has a positive parabolic shape in KHSO while the
4
ꢁ
ꢁ1
1
17,18)
HSO ions in the unit cell occupy sites of C symmetry. plots of T1 for H in RbHSO and NH HSO crystals
4
1
4
4
4
þ
There are two types of crystallographically different K , as have a negative parabolic shape. Therefore, by the Bloem-
well as HSO , ions in the cell. According to the crystal bergen–Purcell–Pound (BPP) theory,
structure data, one kind of HSO ion appears to form a chain slope of T for H in KHSO at about 210 K is not believed
of similar units whereas two units of the other kind of HSO4
ꢁ
19)
the change in the
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ꢁ
1
4
1
4
ꢁ
1
4 4
to be related to HSO motion. The trend of H in KHSO
ion occupy positions at opposite sides of a point of inversion, crystals is not usual. In order to check the phase transition
1
)
forming a dimer through two intermolecular H-bonds.
temperature, we measured differential scanning calorimetry
Recently, we reported on the 39K nuclear magnetic (DSC) using a Du Pont 2010 DSC instrument measurements.
resonance (NMR) at room temperature. The EFG tensors From this result, KHSO showed four phase transitions in
4
of K(1) and K(2) were asymmetric and the orientations of the temperature range from 140 K to 473 K: 451, 453, 456,
the principal axes of the EFG tensors did not coincide for the and 462 K.
K(1) and K(2) sites. These results show that the K(1) and the
K(2) sites, which are surrounded by nine oxygen atoms,
were clearly distinguished by 39K NMR. KHSO4 crystals
7)
have previously been studied by means of X-ray diffrac-
6
,8)
9–12)
tion,
scattering measurements.
electron paramagnetic resonance
1
and Raman
3–15)
In order to obtain information about the dynamic motions
of the HSO4 ion, it is necessary to measure the spin–lattice
relaxation times, T1, of 1H and K in KHSO4 single
crystals. However, very few NMR studies relating to the
39
1
6)
dynamic motion of the oxygen atoms have been reported.
In this paper, the temperature dependences of the spin–
1
39
lattice relaxation time, T , for the H and the K nuclei in a
1
KHSO single crystal grown by using the slow evaporation
4
ꢀ
ꢁ1
,
Corresponding author.
E-mail: aeranlim@hanmail.net, ARL29@cornell.edu
Fig. 1. Temperature dependence of the spin–lattice relaxation rate, T1
1
for H in a KHSO4 single crystal.
1
308

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J. Phys. Soc. Jpn., Vol. 72, No. 5, May, 2003
SHORT NOTES
A. R. LIM et al.
1309
spin–lattice relaxation rate for random motions of the
Arrhenius type with a correlation time ꢀc is described in
terms of fast motion regime in the temperature range of
1
!
60 K to 400 K. The fast motion region can be described as
ꢁ
1
0ꢀc ꢃ 1, T ꢄ exp½Ea=RTꢅ, where !0 is Larmor frequen-
1
cy and Ea is the activation energy. The activation energy
obtained from portions of the log T1 vs 1000/T curve in this
temperature range was 5.65 kJ/mol.
The spin–lattice relaxation time for the 1H nucleus is
relatively long over the entire temperature range while that
3
9
for the K nucleus is short. Based on the BPP theory, the
1
Fig. 2. NMR spectrum of 39K in a KHSO4 single crystal.
change in the slope of T1 for H in KHSO4 at about 210 K is
not believed to have anything to do with HSO4 motion. The
1
change in the curve of the H spin–lattice relaxation time
39
The NMR spectra of 39K in a KHSO4 crystal at room
temperature are shown in Fig. 2. The zero point in Fig. 2
corresponds to the resonance frequency 18.672 MHz of the
K nucleus, and the intensities of the four resonance lines
are similar. Figure represents the central transition
near 210 K is still not completely understood. The K spin–
lattice relaxation behavior is dominated by a phonon
mechanism. The temperature dependence in Fig. 3 can be
k
20)
3
9
ꢁ1
described with the simple power law T1 = A + BT .
Least-squares fits for our data gave a value of k ¼ 2 for the
3
9
39
(
þ1=2 $ ꢁ1=2) of K NMR. The satellite lines for
K
39
K nucleus. Among the phonon processes, the Raman
nucleus, which correspond to the transitions (ꢁ3=2 $
process with k ¼ 2 is considered to be more effective than
the direct process for nuclear quadrupole relaxation. The
temperature dependence of the relaxation rate is in accor-
dance with that for the Raman process of nuclear spin–lattice
ꢁ
1=2) and (þ1=2 $ þ3=2) are out of range. Instead of
39
the one central resonance line of the K nucleus, four
central resonance lines obtained in the case of the KHSO4
crystal. This result points to the existence of two types of
crystallographically inequivalent K(1) and K(2). The four
central resonance lines correspond to two resonances in the
K(1) nucleus and two resonances in the K(2) nucleus, all of
1
39
relaxation. The H and the K NMR results from the
KHSO4 crystals used here did not show any phase transition
between 140 K and 400 K. Consequently, KHSO4 single
crystals may have different properties, which of them are
related to defects and impurities etc.
7
)
which are caused by magnetically inequivalent sites.
The recovery traces of 39K were obtained as a function of
time t at several temperatures and a frequency of
This work was supported by grant No. R05-2001-000-
0148-0 from the Basic Research Program of the Korea
0
Science and Engineering Foundation.
18.672 MHz. These traces are explained by a single
exponential function. The temperature dependence of the
ꢁ
1
39
nuclear spin–lattice relaxation rate, T1 , for K is shown in
Fig. 3. The values of T for the four resonance lines of the
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and F. El-Kabbany: Mater. Res. Bull. 29 (1994) 317.
1
3
9
K nucleus are very similar, within the error range. The
spin–lattice relaxation times are short: T1 ¼ 287 ms and
2
3
4
5
)
)
)
)
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T1 ¼ 2846 ms at 400 K and 200 K, respectively. The tem-
3
9
perature dependence of the relaxation rate for K is
2
proportional to the T as shown by solid line in Fig. 3, so
based on the above theory and the experimental results, the
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(2001) 3511.
7
)
relaxation behavior of 39K in KHSO single crystals can be
explained by the Raman process. In simple NMR theory, the
4
8
9
)
)
F. Payan and R. Haser: Acta Crystallogr. Sect. B 32 (1976) 1875.
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1
1
(
6
Fig. 3. Temperature dependence of the spin–lattice relaxation rate, T1 1,
ꢁ
20) A. Abragam: The Principles of Nuclear Magnetism (Oxford University
Press, Oxford, 1981).
for 39K in a KHSO4 single crystal.