Takasuke Matsuo

Calorimetric and IR spectroscopic studies of phase transitions in methylammonium trihalogenoplumbates (II)

Abstract Heat capacities of CH 3 NH 3 PbX 3 (X = Cl, Br, I) were measured between 13 and 300 K (365 K for the iodide). Two anomalies were found in the chloride and the iodide, and three in the bromide. All the phase transitions were of the first order, although the highest temperature transitions in the bromide and the iodide were close to second order. Their temperatures and entropies are as follows: CH 3 NH 3 PbCl 3 : 171.5 K (14.6 J K −1 mol −1 ), 177.2 K (10.0 J K −1 mol −1 ); CH 3 NH 3 PbBr 3 : 148.8 K(11.2 JK −1 mol −1 ), 154.0K(4.1 J K −1 mol −1 ), 236.3 K (8.2 J K −1 mol −1 ); CH 3 NH 3 PbI 3 : 161.4 K (19.0 J K −1 mol −1 ), 330.4 K (9.7 J K −1 mol −1 ). The transition entropies indicated that the phase transitions are of the order-disorder type. They are interpreted with three possible models involving the methylammonium ions disordered with respect to the orientation of the C-N axis itself and around the C-N axis. The infrared line width of the v 12 vibration of the methylammonium ion depended markedly on the temperature and was interpreted as caused by the hindered rotational motion in the cubic and tetragonal phases.

Dielectric study of CH3NH3PbX3 (X=Cl, Br, I)

Abstract Complex dielectric permittivities of CH3NH3PbX3 (X = Cl, Br, I) were measured at frequencies between 20 Hz and 1 MHz and at temperatures between 20 and 300 K (15 and 350 K for the iodide). Discontinuities or a sharp bend of the real part of the dielectric permittivity occurred at the phase transitions, except at the tetragonal (I4mcm-cubic phase transition where the permittivity showed no apparent change. The dielectric behavior in the cubic and tetragonal (I4mcm phases are described well by a modified Kirkwood-Frohlich equation. Dielectric dispersions were found in the orthorhombic phase of CH3NH3PbBr3 and CH3NH3PbI3 at temperatures between 30 and 120 K.

Calorimetric study of the glassy state X. Enthalpy relaxation at the glass-transition temperature of hexagonal ice☆

Abstract Heat capacities of hexagonal ice were measured with an adiabatic calorimeter. Anomalous temperature drifts and the corresponding C s T hump were observed around 100 K. The sample was then annealed at constant temperatures between 85 and 110 K and the spontaneous temperature change during the annealing was followed. The anomalies were found to be dependent upon the annealing conditions. This thermal behavior is quite similar to that of a glass around the glass-transition temperature. If these phenomena are regarded as the initiation of the proton-ordering process, the configurational entropy change down to 89.4 K, configurational entropy for completely disordered pattern, (3.41 ± 0.22) J K−1 mol−1, and activation enthalpy for the ordering process, (22±4) kJ mol−1, are obtained.

Calorimetric study of phase transition in hexagonal ice doped with alkali hydroxides

Abstract Heat capacities of hexagonal ices doped with 0.1, 0.01, 0.001 mol dm −3 KOH and with 0.1 mol dm −3 RbOH were measured by an adiabatic calorimeter in the temperature range 13 and 300 K. All the specimens showed a phase transition around 72 K. The transition is characterized by the first-order nature and high-temperature tail of the heat capacity anomaly. The largest entropy of transition was 2.33 JK −1 mol −1 . Thus, a substantial part of the configurational entropy of the protons in connection with the half-hydrogen model was removed by the phase transition. The transition took place at essentially the same temperature, irrespective of the concentration and kind of the dopants. These observations led us to conclude that the phase transition was an intrinsic equilibrium property of ice crystals which has so far escaped observation for kinetic reason and which has now revealed itself by the catalytic action of the dopants.

Calorimetric study of a phase transition in D2O ice Ih doped with kod: ice XI

Abstract D2O ice Ih doped with KOD was found by calorimetry to undergo a phase transition at 76 K. The enthalpy and entropy of the phase transition depended in their magnitude on the annealing of the sample. The largest values obtained were ΔH = 155 J mol−1 and δS = 2.06 J K−1 mol−1. The phase transition removed 64% of the residual entropy. Mechanisms of the isotope effect were discussed to explain the difference in the transition temperatures of the D2O and H2O ices and compared with the experiment. The pressure coefficient of the transition temperature was calculated by the use of the Clapeyron-Clausius equation and recent data on the molar volume of the new phase. The name ice XI is proposed to designate the ordered phase of ice Ih.

Heat capacity and glass transition of pure and doped cubic ices

Abstract Heat capacities of pure and KOH (mole fraction 1.8 × 10 −3 )-doped cubic ices were measured at nearly atmospheric pressures in the temperature ranges of 12–160 K and of 80–160 K, respectively. They were prepared from water at 250 MPa through the high pressure ice III and IX. The preparation and the subsequent heat capacity measurement were performed within a cell of an adiabatic high pressure calorimeter. A new glass transition, where the heat capacity showed a jump of 0.1 J K −1 mol −1 , was found at 140 K in the pure ice. The KOH doping caused a decrease in the glass transition temperature by about 30 K. For the bulk samples which had little surface, the enthalpy change during the irreversible cubic-hexagonal transformation at about 200 K was determined to be −(37.0 ± 0.8) J mol −1 . With the heat capacity data of the cubic and hexagonal ices, this value was converted to the enthalpy difference at OK, −(35.6 ± 0.8) J mol −1 .

p-T phase relations of CH3NH3PbX3 (X = Cl, Br, I) crystals

Abstract Pressure-temperature phase relations of CH 3 NH 3 PbX 3 (X = Cl, Br, I) crystals were studied by using a high pressure DTA apparatus in the range between 0.1 Pa and 200 MPa. A triple point was found in each compound below 100 MPa. By pressurization, the low pressure phases disappeared at the triple point in the chloride and bromide while a new high-pressure phase appeared in the iodide. The pressures and temperatures of the triple points are 75.1 MPa, 175.7 K for CH 3 NH 3 PbCl 3 , 43.2 MPa, 152.9 K for CH 3 NH 3 PbBr 3 , and 84.8 MPa, 176.2 K for CH 3 NH 3 PbI 3 . All the boundaries between the cubic and tetragonal phases are upward convex and that of the iodide has a maximum at about 120 MPa. Other phase boundaries are essentially straight lines in the measured pressure and temperature ranges. By the use of the Clausius-Clapeyron equation, the transition volumes were calculated from the slopes of the phase boundaries and the transition entropies obtained in a previously published calorimetric experiment ( J. Phys. Chem. Solids 51 , 1383 (1990)).

Calorimetric and dielectric studies of a phase transition in thallium dihydrogen phosphate: A nearly critical case

Abstract The heat capacity of thallium dihydrogen phosphate was measured from 12 to 300 K. A lambda anomaly with a small first order discontinuity was found at 229.76 K with the integrated enthalpy and entropy changes equal to 370 J mol-1 and 1.8 J K-1 mol-1, respectively. The entropy discontinuity at the first order transition is 0.25 J K-1 mol-1. The Landau theory of phase transitions of the second kind reproduces closely the temperature dependence of the anomalous heat capacity. This, together with the small discontinuity in the entropy, implies that the phase transition is close to a classical critical point of higher order. The relative dielectric permittivity ϵr(b) along the b-axis at 1 kHz is anomalously large and strongly temperature dependent, while the ϵr(a∗) and ϵr(c) are not. A broad absorption centered at 1700 cm-1 was observed in the infrared absorption spectrum, indicating presence of hydrogen bonding of the length ∼ 0.25 nm. Occurrence of a phase transition at 127 ± 2 K was suggested by differential thermal analysis of thallium dideuterium phosphate.

Phase Transitions in the Quinol Clathrate Compounds. I. The Quinol Hydrogen Cyanide Clathrate Compound

The heat capacity of the clathrate compound of quinol with hydrogen cyanide was measured from 12 to 300 K. It exhibited a well defined anomaly at 177.8+0.1 K. The entropy change associated with it was estimated to be 5.71±0.3 J/mol K. This value is close to Rln2, implying that the anomalous heat capacity is due to the order-disorder phase transition concerned with the orientation of the trapped molecules. Dielectric study supported this view. Far infrared spectra of the crystal was recorded from 38 to 500 cm -1 over a range of temperature. Two bands at 46 and 95 cm -1 were found to be characteristic of this substance. A possible assignment of the former band was proposed. Finally, the lattice sum calculation showed that the dipole interaction energy between the guest molecules corresponds to 318 K of temperature compared with the observed transition temperature.

Calorimetric study of pure and KOH-doped tetrahydrofuran clathrate hydrate†

Abstract The heat capacity of pure tetrahydrofuran (THF) clathrate hydrate was measured by an adiabatic calorimeter in the temperature range of 12–300 K. A glass transition having a heat capacity jump of 1.1 J K −1 (H 2 O-mol) −1 was newly observed at 85 K. Combined with previous dielectric data, this was shown to be related to proton configurational motion in the host hydrogen-bonded lattice. The experimental heat capacity of KOH-doped THF-hydrate reported in the previous paper was converted to the molar one of the hydrate by measuring its eutectic melting and making appropriate correction for unreacted ice and THF. Comparison of the heat capacities and entropies of the pure and KOH-doped samples gave new information on the mechanism of the transition observed in the KOH-doped sample.