Orientational and positional disorder of ions and its freezing in the CsNO2-TlNO2 system2

The heat capacities of Cs_0.695Tl_0.305NO₂ (Specimen I) and Cs_0.385Tl_0.615NO₂ (Specimen II) have been measured between 14 and 350 K. Specimen I underwent a phase transition at (197.7 ± 0.1) K, with ΔS = (19.2 ± 1.5) JK^?mol^?, and specimen II at (214.5 ± 0.2) K, with ΔS = (5.4 ± 1.0) JK^?1mol^?1, respectively. Above the phase transition, an exothermic temperature drift due to phase separation was observed. Annealing of the sample at 203 K for 300 hr brought about complete phase separation. The solid solution system annealed at 203 K gave two heat capacity peaks at (203.3 ± 0.1) K, with ΔS = (13.8 ± 0.8) JK^?1 mol^?1, and (242.4 ± 0.2) K, with ΔS = (10.6 ± 1.3) JK^?1 for Specimen I, and at (203.0 ± 0.1) K with ΔS = (6.7 ± 0.5) JK^?1 mol^?1, and (257.5 ± 0.2) K with ΔS = (17.9 ± 1.7) JK^?1 mol^?1 for Specimen II. The phase diagram of the CsNO₂-TlNO₂ binary system was constructed on the basis of DTA, heat capacity and dielectric measurements. In the metastable phase, the existence of a residual entropy due to the freezing of a random distribution of Cs⁺₁ and Tl⁺ cations in addition to the orientational disorder of the NO₂^?1 ion was confirmed by a comparison of entropies of the stable and the metastable phases.     

The heat capacity of the layer compounds (CH3CH2CH2NH3)2MnCl4 and (CH3CH2CH2NH3)2CdCl4 from 10 K TO 300 K

The heat capacity of the layer compounds tetrachlorobis (n-propylammonium) manganese II and tetrachlorobis (n-propylammonium) cadmium II, (CH₃CH₂CH₂NH₃)₂MnCl₄ and (CH₃CH₂CH₂NH₃)₂CdCl₄ respectively, has been measured over the temperature range 10 K ?T ? 300 K.Two known structural phase transitions were observed for the Mn compound in this temperature region: at T = 112.8 ± 0.1 K (ΔH_t= 586 ± 2 J mol^?1; ΔS_t = 5.47 ± 0.02 J K^?1mol^?1) and at T =164.3 ± (ΔH_t = 496 ± 7 J mol^?1; ΔS_t =3.29 ± 0.05 J K^?1mol^?1). The lower transition is known to be from a monoclinic structure to a tetragonal structure, while the upper is from the tetragonal phase to an orthorhombic one. From comparison with the results for the corresponding methyl Mn compound it is deduced that the lower transition primarily involves changes in H-bonding while the upper transition involves motion in the propyl chain.A new structural phase transition was observed in the Cd compound at T= 105.5 ± 0.1 K (ΔH_t= 1472.3 ± 0.1 J mol^?1; ΔS_t = 13.956 ± 0.001 J K^?1mol^?1), in addition to two transitions that have been observed previously by other techniques. The higher of these transitions(T = 178.7 ± 0.3 K; ΔH_t = 982 ± 4 J mol^?1 ΔS_t = 6.16 ± 0.02 J K^? mol^?1) is known to be between two orthorhombic structures, while the structural changes at the lower transition (T= 156.8 ± 0.2 K; ΔH_t = 598 ± 5 J mol^?1, ΔS_t = 3.85 ± 0.03 J K^?1 mol^?1) and at the new transition are not known. It is proposed that these two transitions correspond respectively to the tetragonal to orthorhombic and monoclinic to tetragonal transitions in the propyl Mn compounds.In addition to the structural phase transitions (CH₃CH₂CH₂NH₃)₂MnCl₄ magnetically orders at t? 130 K. The magnetic contribution to the heat capacity is deduced from the heat capacity of the corresponding diamagnetic Cd compound and is of the form expected for a quasi 2-dimensional Heisenberg antiferromagnet.     

Low temperature thermal properties of PbI2

The heat capacity and thermal conductivity of a large (56.5 g) crystal of PbI₂ have been measured in the temperature region 0.5 < T < 3.9°K. Analysis of the heat capacity data yields a value of the limiting apparent Debye characteristic temperature θ₀^c = 99.4 (±0.3)°K, which corresponds to an average lattice wave velocity of 1.151 (±0.005) × 10⁵ cm sec^?1. It is consistent with a wave velocity estimated from neutron scattering experiments, but not with one determined from Brillouin spectra. The heat capacity data also show that dispersion of the low frequency waves is not unusual, as might have been expected for a layer-type crystal. The apparent thermal conduction is found to be surprisingly small in the crystal.     

The heat capacity of the layer compound tetrachlorobis (methylammonium) manganese—II (CH3NH3)2MnCl4, from 10 to 300k

The heat capacity of the layer compound, tetrachlorobis (methylammonium) manganese II, (CH₃NH₃)₂MnCl₄, has been measured over the range 10K <T<300K. In this region, two structural phase transitions have been observed previously by other techniques: one transition is from a monoclinic low temperature (MLT) phase to a tetragonal low temperature (TLT) phase, and the other is from TLT to an orthorhombic room temperature (ORT) phase. The present experiments have shown that the lower transition (MLT→TLT) occurs at T = 94.37±0.05K with ΔH_t = 727±5 J mol^?1 and ΔS_t = 7.76±0.05 J K^?1 mol^?1, and the upper transition (TLT→ORT) takes place at T = 257.02±0.07K with ΔH_t = 116±1J mol^?1 and ΔS_t = 0.451±0.004 J K^?1mol^?1. These results are discussed in the light of recent measurements on (CH₃NH₃)₂CdCl₄, and also with regard to a recent theoretical model of the structural phase transitions in compounds of this type.In addition to the structural phase transitions, (CH₃NH₃)₂MnCl₄ also undergoes magnetic ordering at T < 150K. The magnetic component to the heat capacity, as deduced from a corresponding states comparison of the heat capacity of the present compound with that of the Cd compound, is shown to be consistent with the behaviour expected for a quasi 2-dimensional Heisenberg antiferromagnet.     

Heat capacities of copper(II) formate tetrahydrate and tetradeuterate: A comparative study of phase transitions in layer hydrate crystals

The heat capacities of copper(II) formate tetrahydrate and tetradeuterate have been measured from 12 to 300 K with an adiabatic calorimeter. They have sigmoidal temperature dependence except near the antiferroelectric-paraelectric transition temperatures, 235.78 ± 0.05 K and 245.64 ± 0.05 K, respectively. The corresponding enthalpy changes are 836.0 ± 1.0 J mol^?1 and 936.9 ± 0.5 J mor^?1. The entropy changes are 3.546 ± 0.005 JK^?1mol^?1 and 3.814 ± 0.002 JK^?1 mol^?1. The heat capacities are larger in the high temperature phase than in the low temperature phase, the difference amounting to 5.74 JK^?1 mol^?1 and 7.15 JK^?1 mol^?1 for the hydrate and the deuterate, respectively. The heat capacity anomaly is compared with those in tin(II) chloride dihydrate and potassium hexacyanoferrate trihydrate and discussed in relation to the structure of the hydrogen bond networks in these substances. The discussion is extended to include possible properties of the hydrogen bond frameworks in ices I_h and II.     

Possible observation of the coexistence of superconductivity and long-range magnetic order in NdRh4B4

The ternary rare earth compound NdRh₄B₄ has been studied by means of critical field, low temperature heat capacity, and static magnetic susceptibility measurements. Features in the upper critical field and heat capacity data at 1.31 K and 0.89 K suggest the occurrence of long-range magnetic order in the superconducting state. The temperature dependence of the static magnetic susceptibility follows a Curie-Weiss law with an effective magnetic moment μ_eff = 3.58 ± 0.05 μ_B and a Curie-Weiss temperature θ_p = ?6.2 ± 1.0 K between 20 K and room temperature. However,, magnetization vs. applied magnetic field isotherms suggest the development of a ferromagnetic component in the Nd³⁺ magnetization at low temperatures.     

Heat capacity anomalies due to successive phase transitions in 1,1′-biphenyl

Precision heat capacity measurements on 1,1′-biphenyl revealed two broad anomalies at 11.0 K and 40.4 K. The excess enthalpies and entropies are 0.28 ± 0.02 J mol^?1 and 0.026 ± 0.002 J K^?1mol^?1 for the anomaly extending from 7.5 to 14.0 K, and 5.02 ± 0.08 J mol^?1 and 0.129 ± 0.003 J K^?1mol^?1 for the anomaly extending from 30.0 to 47.0 K, respectively. A possible molecular mechanism is suggested.     

Thermal evidences for successive CDW phase transitions in 1T-TaS2

The heat capacity of 1T-TaS₂ has been measured over the temperature range including the successive phase transitions (140 K–370 K) by an adiabatic calorimeter. There are three transitions in the measured temperature range, two first-order transitions (at about 226 K (T₁) and about 353.5 K (T₃)) and one small anomaly at about 283 K (T₂) with a broad peak. The transition enthalpies are as follows; ΔH₁=52±5 cal·mol^-1, ΔH₂=7.5±2 cal· mol^-1 and ΔH₃=122±8cal·mol^-1.     

Specific heat of YBa2Cu3O7−x from 4.2 to 60 K

The specific heat of superconducting oxide compound, YBa₂Cu₃O_{7 ?x} , is studied using a quasi-adiabatic calorimeter from 4.2 to 60 K. The analysis of the specific heat data below 15 K gives a value of 17 mJ/mole K² for the electronic heat capacity coefficient. The value ofθ _D(0) is determined to be 397±8 K. The variation ofθ _D with temperature was calculated in the temperature range 4.2 to 60 K.     

Crystal structure and thermochemical properties of phase change materials bis(1-octylammonium) tetrachlorochromate

A new crystalline complex (C₈H₁₇NH₃)₂CdCl₄(s) (abbreviated as C₈Cd(s)) is synthesized by liquid phase reaction. The crystal structure and composition of the complex are determined by single crystal X-ray diffraction, chemical analysis, and elementary analysis. It is triclinic, the space group is P-1 and Z = 2. The lattice potential energy of the title complex is calculated to be U_POT (C₈Cd(s))=978.83 kJ·mol^-1 from crystallographic data. Low-temperature heat capacities of the complex are measured by a precision automatic adiabatic calorimeter over a temperature range from 78 K to 384 K. The temperature, molar enthalpy, and entropy of the phase transition for the complex are determined to be 307.3± 0.15 K, 10.15± 0.23 kJ·mol^-1, and 33.05± 0.78 J·K^-1·mol^-1 respectively for the endothermic peak. Two polynomial equations of the heat capacities each as a function of temperature are fitted by the least-square method. Smoothed heat capacity and thermodynamic functions of the complex are calculated based on the fitted polynomials.     

Heat capacity of a five-coordinated iron(III) complex with spin S = 32, bromobis(N,N-diethyldithiocarbamato)iron(III), between 0.4 and 300 K

Heat capacity measurements have been made for six kinds of specimens prepared by different methods. Among them, Sample A exhibited a A-type ferromagnetic pahse transition at 1.347 K and a Schottky-type anomaly due to the zero-field splitting around 9K. The total entropy and enthalpy were (11.05 ± 0.04) J K^?1mol^?1 and (97.0 ± 0.4) J mol^?1, respectively. Sample B exhibited a Sehottky-type anomaly around 0.4 K due to the ferro-magnetic dimeric coupling with $\text{J}{}_{\mathrm{D}}\text{k}\text{= + 0.30}\text{K}$ as well as the Schottky-type anomaly at 9K. The total magnetic entropy and enthalpy were (11.45 ± 0.03) JK^?1 mol^?1 and (93.8 ± 0.8) J mol^?1, respectively. The remaining samples are simple mixtures of the λ-type modification and the dimeric modification. Irrespective of the magnetic behavior at low temperatures, all the samples showed a non-magnetic first-order phase transition around 270 K. The heat capacity and entropy of this phase transition have been accounted for in terms of the Frenkel theory of heterophase fluctuation. Construction of an adiabatic-type calorimeter workable between 1.5 and 393 K has been also presented.     

Specific heat of single phase Nb3Ge

For the first time, the specific heat of single phase, stoichiometric, high transition temperature (21.8 K) A-15 Nb₃Ge has been measured. From the data between 4 and 29 K, the linear term coefficient, γ, of the specific heat is found to be 30.3±1. mJ/mole-K² and the Debye temperature, ?_D, is 302±2 K. The bulk energy gap parameter, 2Δ/kT_c, is found to be 4.2±0.2, in agreement with tunneling measurements.     

The specific heat of CeAl2 between 0.02 and 1 K

We report specific heat measurements on a CeAl₂ single crystal between 0.02 and 1 K. Above 0.08 K, we found C₀ = γT + βT³ with γ = (130±0.5) mJ/K²mole and β = (142±1) mJ/K⁴mole in good agreement with previous results above 0.3 K. Below 0.08 K, an excess specific heat C_N = αT^?2 with α = (6.4±1) mJK/mole was detected and interpreted in terms of hyperfine splitting of the Al²⁷ nuclear states. Our results suggest that in CeAl₂ (complex) antiferromagnetism coexists with the Kondo effect at least down to 20 mK.     

Gas phase high temperature photoelectron spectroscopy: an investigation of the transition metals scandium and vanadium

The He(I) photoelectron spectra of atomic scandium and vanadium have been recorded in the gas-phase. For scandium two bands associated with a (4s)^?1 ionization and one band associated with a (3d)^?1 ionization of the neutral atom have been observed. Measurement of their relative intensities allows the σ_3d:σ_4s photoionization cross-section ratio in atomic scandium to be estimated as 57.1 ± 9.0. In the atomic vanadium spectrum, six bands were seen. Four of these correspond to (3d)^?1 and (4s)^?1 ionizations of the ground state of the neutral atom, the V a⁴F state, whereas two bands correspond to (3d)^?1 ionizations of an excited state, the V a₆D state, which is approximately 2100 cm^?1 above the ground state. Measurement of the intensities of bands arising from the V a₄F state allows σ_3d:σ_4s to be estimated as 29.8 ± 2.5 for vanadium. Spectra of vanadium have been recorded with both single- and multi-detector photoelectron spectrometers. Comparison of the data acquisition rates obtained with both spectrometers demonstrates the advantage of using a multidetector instrument in high temperature photoelectron spectroscopy.     

Heat capacity of a five-coordinated ferromagnet,chloro bis(N,N-diethyldithiocarbamato)iron(III), in the temperature range from 0.4 to 20 K

The heat capacity of polycrystalline Fe[S₂CN(C₂H₅)₂]₂Cl has been measured in the temperature range from 0.411 to 19.55 K. The transition between ferromagnetic and paramagnetic states is characterized by a sharp λ-type anomaly centered at the Curie temperature, T_c = 2.412 ± 0.008 K. The enthalpy and the entropy of transition are 40.475 J mol^?1 and 11.199 J K^?1mol^?1 (= 1.347 R), respectively. The transition entropy is only 2.81% smaller than R In 4. This fact ascertains that the spin manifold is really a quartet. The ground spin states of the present compound are characterized by a zero-field splitting of the $\text{S =}\text{3}\text{2}$ state into two Kramers' doublets. The overlapping non-cooperative Schottky-type anomaly due to the energy separation between the two Kramers' doublets is separated tentatively from the cooperative heat capacity due to the exchange interaction. Based on a careful analysis of the transition entropy it may be concluded that the magnetic structure of the present complex would be a two-dimensional triangular Ising lattice. The exchange and the Curie-Weiss constants are also determined to be 0.155 and 4.19 K, respectively.     

Heat capacity behaviour of Pu−Fe eutectic alloy (10 a/o Fe) between 15 and 373°K. Evidence for order-disorder and an antiphase structure below room temperature

Low temperature heat capacity studies of Pu?Fe eutectic alloy (10 a/o Fe) have suggested the possibility of order-disorder of atoms and an antiphase structure below room temperature. Slow cooling and temperature cycling below 76°K were required for appearance of the postulated antiphase structure. Fermi surface-Brillouin zone boundary interactions are suggested as an explanation for the low temperature behavior of the eutectic alloy as well as for the resistivity maximum in both Pu₆Fe and α-Pu. The best values for S°(298) and {H°(298)?H°(0)} were judged to be 14·20±0·10 cal mol^?1 K^?1 and 1660±30 cal mol^?1.     

Stiffness matrix and debye temperature of ReO3 from ultrasonic measurements

We have measured the propagation velocities of bulk acoustic waves in the simple cubic transition-metal oxide ReO₃ by ultrasonic pulse propagation. The elastic stiffness constants at 300 K are: C₁₁ = (47.9 ± 1.4) × 10¹¹ dyne/cm²; C₄₄ = (6.1 ± 0.2) × 10¹¹ dyne/cm²; C₁₂ = (?0.7 ± 2.8) × 10¹¹ dyne/cm². These elastic constants indicate a crystal with highly anisotropic shear propagation. The Debye temperature of the compound from these measurements is 528 K. This value is somewhat higher than previous results from specific heat and resistivity determinations.     

Phase transition and freezing of ionic disorder in CsNO2 and TINO2 crystals2

The heat capacities of CsNO₂ and TlNO₂ have been measured in the temperature region between 13 and 350 K. The phase transitions of CsNO₂ and TlNO₂ were found at (209.16 ± 0.10)K and (282.4 ± 0.1)K. The enthalpy and entropy of the phase transition were (3.45 ± 0.20) kJ mol^?1 and (17.2 ± 1.0) JK^?1 mol^?1 for the former, and (6.44 ± 0.31) kJ mol^?1 and (23.8 ± 1.1) JK^?1 mol^?1 for the latter. The glass transitions were found around 42 K in CsNO₂ and around 60 K for TlNO₂, respectively. The corresponding dielectric relaxations were observed between 58 and 130 K for CsNO₂ in the frequency range between 10² and 10⁵ Hz and between 80 and 180 K for TlNO₂ in the frequency range between 2 × 10² and 10⁵ Hz. The calorimetric and dielectric relaxation times yielded a straight line in the Arrhenius plot over a wide time scale ranging from 10^?6 to 10⁵ sec. The slope gave the activation enthalpy of 13.8 kJ mol^?1 and 19.5 kJ mol^?1 for CsNO₂ and TlNO₂, respectively. The transition entropy supplemented by a residual entropy R ln 3 for CsNO₂ and R ln 2 for TlNO₂ gave (26.3 ± 1.0) JK^?1 mol^?1 and (29.6 ± 1.1) JK^?1 mol^?1 for the orientational entropy of the NO₂^? ion in the high-temperature phase. Based on the packing and symmetry considerations, these entropies were interpreted by the model which included two different sets of orientations of the NO₂^? ions parallel to [110] and [111] in the CsCl type unit cell. The existence of the different sets of orientation was proved by the doublet (Δv ~ 10 cm^?1) of the Raman spectrum of the bending mode of the NO₂^? ion in the cubic phase of the CsNO₂ crystal. The band narrowed to an ordinary singlet with increasing temperature. This observation was accounted for as the motional narrowing in which the NO₂^? ion felt an averaged field of the two different sets owing to the increased rate of jumping as the temperature increased.     

A calorimetric study of LiClO4 · 3H2O

The heat capacity of LiClO₄ · 3H₂O was measured from 17 to 343 K, in order to determine the relationship between its phase diagram and the phase diagrams of divalent metal perchlorate hexahydrates The heat capacity curve of pure LiClO₄ · 3H₂O was found to be smooth, indicating an absence of polymorphism, although a small amount of excess perchloric acid in one sample gave rise to a eutectic point at 232 8 ± 0 3 K The absence of transitions in LiClO₄ · 3H₂O is discussed in terms of its known structure, and some conclusions are drawn concerning the differences in H-bonding in this salt and in divalent metal perchlorate hexahydrates.     

Assessment of health hazard due to natural radioactivity in Kluang District,Johor, Malaysia

The radiation survey of the ambient environment was conducted using two gamma detectors, and the measurement results were used in the computation of the mean external radiation dose rate, mean-weighted dose rate and annual effective dose, which are 144 nGy h^?1, 0.891 mSv y^?1 and 178 μSv, respectively. A high-purity germanium detector was used to determine the activity concentrations of ²³²Th, ²²⁶Ra and ⁴⁰K in soil samples. The results of the gamma spectrometry of the soil samples show radioactivity concentration ranges from 19±1 to 405±13 Bq kg^?1 with a mean value of 137±5 Bq kg^?1 for ²³²Th, from 21±2 to 268±9 Bq kg^?1with a mean value of 78±3 Bq kg^?1 for ²²⁶Ra and from 23±9 to 1268±58 Bq kg^?1 with a mean value of 207±13 Bq kg^?1 for ⁴⁰K. Radium equivalent activity (Ra_eq) and external hazard index (H_ex) were 290 Bq kg^?1 and 0.784, respectively, which were safe for the population. The mean lifetime dose and lifetime cancer risk for each person living in the area with average lifetime (70 y) were 12.46 mSv and 7.25×10^?4 Sv year, respectively. The results were compared with values given in United Nations Scientific Committee on the Effects of Atomic Radiation 2000.