Kenzi Hukuda

Dielectric and Thermal Study of K2SeO4 Transitions

The behaviours of the various dielectric properties and specific heat of potassium selenate, K 2 SeO 4 , have been studied with particular reference to the transitions at 129.5°K and 93°K. Below 93°K the crystal is ferroelectric along the c axis. The spontaneous polarization and coercive field determined from the hysteresis loop are 6.5×10 -8 coul/cm 2 and 60 V/cm respectively at 80°K. The curve of dielectric constant vs temperature obeys the Curie-Weiss law above the Curie point and the Curie constants for warming and cooling processes are 27°K and 30°K respectively. The Curie temperature varies almost linearly with the biasing field with the coefficient of 0.19°/kV/cm. Effects of the γ-radiation on the dielectric behaviour are observed. Discontinuity of the specific heat of about 2.3 cal/mol·deg has found at the transition of 129.5°K. Anomaly at the transition of 93°K is very small. The transition energy and the entropy change are estimated to be of the order of 0.5 cal/mol and 5×10 -3 cal/mol·deg of le...

Proton Dynamics in KDP Studied by ESR of SeO43

The hyperfine coupling tensor for the close protons of SeO 4 3- in ferroelectric KDP has been determined, the principal values of which are A 1 =12.1 MHz, A 2 =-21.9 MHz and A 3 =-38.0 MHz. Exchange between two polar Slater configurations has been studied by observing proton and Se 77 hyperfine structures in the paraelectric phase near T C . The exchange frequency obtained from the proton hyperfine structure agrees very well with that from the Se 77 hyperfine structure in the whole range of the experimental temperature. The temperature dependence of the exchange frequency can be approximately represented by the Arrhenius law, where the activation energy and the preexponential factor are 0.19 eV and 4.6×10 13 Hz respectively.

Electron Spin Resonance of SeO 4 3− and SeO 3 − Radicals in KDP Single Crystal

X-ray irradiation of KDP-K 2 SeO 4 mixed crystal is shown to produce SeO 4 3- and SeO 3 - radicals. The ESR spectrum of SeO 4 3- has well-resolved proton hyperfine structure which exhibits the “quintet to triplet” transition as seen on AsO 4 4- radical in KDA. This radical may be used as a new “probe” to study the proton dynamics of KDP. The tensors of hyperfine interaction with Se 77 for these radicals are evaluated from the angular dependence of ESR spectra of the radicals. The principal values of the hyperfine tensor of SeO 4 3- are as follows, T // =3389 MHz and T ⊥ =3178 MHs in the paraelectric phase, and T 1 =3055 MHz, T 2 =2986 MHz and T 3 =3490 MHz in the ferroelectric phase.

Electron Paramagnetic Resonance of Cr3+ Ions in Antiferroelectric ADP Crystals

The electron paramagnetic resonance absorption of Cr 3+ ions doped in ADP(NH 4 H 2 P0 4 ) single crystals was studied both in the paraelectric and the antiferroelectric phases. It is found that there is one kind of dominant Cr 3+ ion sites in the crystals in the para phase and that these sites are divided into two slightly different kinds of sites in the antiferro phase. From angular variation of the EPR spectrum, it is inferred that Cr 3+ ions of this sites take substitutionally the positions of NH 4 + ions and have two vacancies of neighboring protons so as to satisfy the charge compensation and the crystal symmetry. The spin Hamiltonian parameters are detarmined as g // = g ⊥ =1.98, | D |=0.100 cm -1 and | E |=0.022 cm -1 151°K. We could explain the line splitting of the EPR spectrum due to the two divided Cr 3+ ion sites, by using the twin structure model which consists of the right-hand a - b system and left-hand a - b system having the c -axis in common.

X-Ray Study of Thermal Parameters of NH4H2PO4 and ND4D2PO4 in the Paraelectric Phase

Thermal parameters of P and N atoms of the antiferroelectric NH 4 H 2 PO 4 (ADP) and the deuterated isomorphous ND 4 D 2 PO 4 (DADP) have been observed as a function of temperature in the paraelect...

Slowing Down of Fluctuation in KDP Studied by ESR on SeO43

Temperature dependence of ESR spectrum on the SeO 4 3- radical substituted for PO 4 3- in KDP(KH 2 PO 4 ) single crystal has been interpreted by the model that locally ordered regions are formed in the paraelectric phase of the crystal as the temperature approaches T c and the polarization of each region fluctuates with the relaxation time τ. Estimated temperature dependence of the fluctuation rate exhibits the slowing down phenomenon near T c which is represented as τ -1 = A ( T - T c ) m with m =0.99.

Deuterium Concentrations of H2PO4- and NH4+ Radicals in Partially Deuterated NH4H2PO4

The deuteration rates (D-rates) of H 2 PO 4 - radicals ( R P ) in partially deuterated NH 4 H 2 PO 4 crystals are measured by ESR of SeO 4 3- doped in the crystals. It is found that the phase transition temperatures ( T c ) of the crystals depend linearly on R p ; T c ( R P ) = 148 + 94 R P [K]. Using this relation and data about total D-rate of highly deuterated ADP obtained by others, D-rates of NH 4 + radicals ( R N ) in the crystals are calculated. It is pointed out that the shift of T c does not depend on R N but on R P .

ESR Observation of Coexistence of Paraelectric and Ferroelectric Phases en DKDP

The ESR spectrum of SeO 4 3- radicals doped in the DKDP single crystal has been found to behave near T c in a manner quite different from those of SeO 4 3- in KDP and Cr 5+ in DKDP. The spectrum consists of two kinds of signals from paraelectric and ferroelectric phases of the crystal in a narrow temperature range around T c . The range is estimated to be about 4 K. Above this range, only high symmetric paraelectric spectrum can be observed and the low symmetric ferroelectric one does not survive in contrast with the results on the KDP: SeO 4 3- and DKDP: Cr 5+ previously reported.

The Kinetics of Radical Reactions in γ-Irradiated Polyvinyl Chloride

The rates of production and extinction of radicals in gamma irradiated polyvinyl chloride were studied by means of electron spin magnetic resonances at 3 cm wavelength. The radical reaction constants lambda and lambda 2 were estimated to be 18 and 4 kcal/mole, respectively.

Behavior of 77Se Hyperfine Components of SeO43- Radicals in Highly Deuterated NH4H2PO4

The authors observed the 77 Se hyperfine (hf) components of ESR spectrum of SeO 4 3- radicals doped in 94%-deuterated NH 4 H 2 PO 4 (D 0.94 ADP) and compared the result with those for D x ADP (0≦ x ≦0.70) crystals. In tlte paraelectric phase no remarkable deuteration effect was observed. In the antiferroelectric (AFE) phase, on the other hand, a new type of angular dependence of the hf line-position was found between about 185 K and T c (236 K). The results mean that the crystal field of the AFE host crystal which distorts the SeO 4 3- into the AFE configuration depends on temperature remarkably in the AFE D 0.94 ADP.