Michio Sorai

Phonon coupled cooperative low-spin 1A1high-spin 5T2 transition in [Fe(phen)2(NCS)2] and [Fe(phen)2(NCSe)2] crystals

Abstract Heat capacities of [Fe(phen) 2 (NCS) 2 ] and [Fe(phen) 2 (NCSe) 2 ] were measured between 13 5 and 375 K. A heat capacity anomaly due to the spin-transition from low-spin 1 A 1 to high-spin π 2 electronic ground state was found at 176·29 K for the SCN-compound and at 231·26 K for the SeCN-compound, respectively. Enthalpy and entropy of transition were determined to be Δ H = 8·60 ± 0·14 kJ mol −1 and Δ S = 48·78 ± 0·71 J K −1 mol −1 for the SCN-compound and Δ H = 11·60 ± 0·44 kJ mol −1 and Δ S = 51·22 ± 2·33 J K −1 mol −1 for the SeCN-compound. To account for much larger value of Δ S compared with the magnetic contribution, we suggest that there is significant coupling between electronic state and phonon system. We also present a phenomenological theory based on heterophase fluctuation. Gross aspects of magnetic, spectroscopic, and thermal behaviors were satisfactorily accounted for by this model. To examine closely the transition process, infrared spectra were recorded as a function of temperature in the range 4000 − 30 cm −1 . The spectra revealed clearly the coexistence of the 1 A 1 , and the 5 T 2 ground states around T c .

Heat Capacity of [Cr4(OH)6(en)6](SO4)3·10H2O from 1.4 to 200 K and Spin Interaction

The heat capacity was measured between 1.4 and 200 K. The magnetic contribution was determined by subtracting the lattice contribution from the overall heat capacity with the aid of effective frequency distribution function. The magnetic heat capacity showed two peaks at 2.3 K and at about 20 K. These features are satisfactorily accounted for by assuming a spin Hamiltonian of the form, \(\mathscr{H}{=}-J(\textbf{\itshape S}_{1}{\cdot}\textbf{\itshape S}_{3})-j[(\textbf{\itshape S}_{1}{\cdot}\textbf{\itshape S}_{2})+(\textbf{\itshape S}_{2}{\cdot}\textbf{\itshape S}_{3})+(\textbf{\itshape S}_{3}{\cdot}\textbf{\itshape S}_{4})+(\textbf{\itshape S}_{4}{\cdot}\textbf{\itshape S}_{1})]-J_{24}(\textbf{\itshape S}_{2}{\cdot}\textbf{\itshape S}_{4})\). The closest agreement between theory and experiment was obtained for J =-42.6 k , j =-22.8 k and J 24 =-7.6 k . The sign of the parameters indicates that all the spin interactions are antiferromagnetic. It was concluded that one need not introduce any higher-order ...

Update 1 of: calorimetric investigation of phase transitions occurring in molecule-based magnets.

Occurring in Molecule-Based Magnets† Michio Sorai,*,‡ Yasuhiro Nakazawa,‡,§ Motohiro Nakano, and Yuji Miyazaki‡ ‡Research Center for Structural Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan

Heat Capacity of N-(o-Hydroxy-p-Methoxybenzylidene)-p-Butylaniline: A Glassy Nematic Liquid Crystal

Abstract The heat capacity of N-(2-hydroxy-4-methoxybenzylildene)-4′-butylaniline(2,4-OHMBBA) with a purity of 99.393 mole % was measured between 13 and 375 K. The Melting point T m was 314.30 K, and the enthalpy and the entropy of fusion were 22.405 kJ mol−1 and 71.425 J K−1 mol−1, respectively. The temperature of transition from nematic to isotropic liquid was 33.65 ± 0.1 K, and the enthalpy and the entropy changes due to this mesophase transition were 887.4 ± 4.9 J mol−1 and 2.690 ± 0.015 J K−1 mol−1, respectively. A second-order character has been postulated for the mesophase transition. By cooling the nematic liquid crystal at a rate of − 12.2 K min−1 a frozen-in state of the stable nematic phase, i.e. a glassy state, was realized. The glass transition temperature Tg was 204 K and the heat capacity jump at T g was Δ C = 107 J K−1 mol−1. The activation enthalpy for the glass transition was estimated to be Δ H = 75 kJ mol−1. The residual entropy of the glassy state at O K was determined to be 12.69 ± 0...

Magnetic and Thermal Properties of Crystals Including Isolated Clusters. I. Heat Capacity and Infrared Spectrum of [Cr3O(CH3COO)6(H2O)3]Cl·6H2O Crystal between 1.5 and 280 K

The heat capacity was measured between 1.5 and 280 K. At liquid helium temperatures a heat capacity anomaly was observed and a new phase transition was found at 211.4 K with a secondary C p maximum at 215.5 K. The entropy and the enthalpy changes for the overall transition are Δ S t =13.778 J K -1 mol -1 and Δ H t =3322 J mol -1 , respectively. The infrared spectra were measured at 120,225 and 295 K. Many new absorption peaks appeared below the transition point. A mechanism for the phase transition is suggested in terms of ordering processes of crystalline water. A new model is proposed for explaining the heat capacity anomaly at liquid helium temperature: The cluster ions with equilateral triangle symmetry at room temperature are slightly distorted through the phase transition processes resulting two kinds of cluster ions forming isosceles triangles with different exchange parameters. The closest agreement with the experimental data was obtained by assuming J 0 =30 k and J 1 =4.5 k for half moles of the ...

Do alkoxy chains behave like a solvent in the D phase? DSC study of binary systems, ANBC (nC) (nC = 8, 16 and 18)-n-tetradecane

The phase behaviour of the binary systems ANBC(nC)-n-tetradecane, for nC = 8, 16 and 18, was examined using DSC, paying special attention to the role of the alkoxy chain of the ANBC molecule in the D phase. The dependence of the SmC-D and D-isotropic liquid transition temperatures upon the apparent average number of paraffinic carbon atoms closely resembles the nC dependence in the series of neat ANBCs, demonstrating that the alkoxy chain behaves, at least in part, like the solvent in lyotropic liquid crystals. The D phase was not detected in ANBC(8)-n-tetradecane.

Complex phase transitions in stable thiazyl radicals: spin-gap, antiferromagnetic ordering and double melting

We examined the magnetic and thermal properties of a stable thiazyl radical 1,3,2-benzodithiazolyl, BDTA. While the diamagnetic room-temperature phase had been known for BDTA, we found a new phase transition to a paramagnetic solid phase at 346 K and a superheating process that resulted in the double melting (melt recrystallization–melt process) above 360 K. The supercooling of the paramagnetic high-temperature phase also occurred, leading to an antiferromagnetic ordering at 11 K with a λ-type anomaly in the temperature dependence of the heat capacity. Based on these data, the complex phase diagram of BDTA has been determined.

Quasi-binary picture of thermotropic liquid crystals and its application to cubic mesophases

Abstract A quasi-binary (QB) picture of thermotropic liquid crystals is proposed on the basis of thermodynamic observations. The experimental conformational entropy of long alkyl chains attached to a (semi)rigid core of mesogenic molecules indicates that the chain is highly disordered in liquid crystalline states. These disordered chains serve as ‘intramolecular solvent’ or ‘self-solvent’ judging from a close resemblance between phase diagrams of neat (against chain length) and binary (against composition) systems. The application of the QB picture to the classic examples of thermotropic cubic mesophases (in ANBC series) shows that the essential structural motif is triply periodic minimal surface.

An automated adiabatic calorimeter for the temperature range 13 K to 530 K The heat capacities of benzoic acid from 15 K to 305 K and of synthetic sapphire from 60 K to 505 K

Construction of a fully automated adiabatic heat-capacity calorimeter which has been successfully operated at temperatures from 13 K to 530 K is reported. This calorimeter has been designed specially so as remarkably to economize liquid helium: 7 dm 3 of liquid helium was enough to cool the apparatus from 77 K to 10 K and to measure heat capacities from 13 K upwards. Its performance has been examined by measurements on the standard reference materials: benzoic acid (NBS SRM39i) from 15 K to 305 K and synthetic sapphire (α-Al 2 O 3 : NBS SRM720) from 60 K to 505 K. The results are compared with those of other investigators. Overall precision assessed as deviations from a smoothed curve is within ±0.0005· C p or better, while the inaccuracy is within ±0.0025· C p except for the temperature regions below about 25 K and above about 400 K.

Observation of superconductivity in heavy-fermion compounds of Ce2CoIn8

We succeeded in growing a single crystal of Ce 2 CoIn 8 by the flux method. The results of specific heat and electrical resistivity measurements indicate that Ce 2 CoIn 8 is a heavy-fermion superconductor below 0.4 K with an electronic specific heat coefficient γ as large as 500 mJ/K 2 mol-Ce.