Anomalous Behavior Of Specific Heat Research Articles

Pairing Reentrance Phenomenon in Heated Rotating Nuclei in the Shell-Model Monte Carlo Approach

Rotational motion of heated 72Ge is studied within the microscopic shell-model Monte Carlo approach. We investigate the angular momentum alignment and nuclear pairing correlations associated with J^{π} Cooper pairs as a function of the rotational frequency and temperature. The reentrance of pairing correlations with temperature is predicted at high rotational frequencies. It manifests itself through the anomalous behavior of specific heat and level density.

Anisotropic superconductivity in Lu2Fe3Si5

We have prepared polycrystalline and single crystalline silicon-containing superconductor Lu2Fe3Si5, and evaluated its superconducting properties. The reduced specific heat jump at the transition temperature and a finite residual electronic specific heat are confirmed. However, magnetization measurements indicate the presence of appreciable paramagnetic background, implying the extrinsic nature of the anomalous specific heat behavior. Remarkable peak effects show up in the magnetization measurements for both polycrystalline and single crystalline samples. A clear anisotropy in the upper critical field classifies Lu2Fe3Si5 into a quasi two-dimensional superconductor.

X-ray absorption studies of the local structure andf-level occupancy inCeIr1−xRhxIn5

The ${\mathrm{CeIr}}_{1\ensuremath{-}x}{\mathrm{Rh}}_{x}{\mathrm{In}}_{5}$ series exhibits a range of interesting phenomena, including heavy-fermion superconductivity, non-Fermi liquid behavior, and concomitant antiferromagnetism and superconductivity. In the low-Rh concentration range $(0.1\ensuremath{\leqslant}x\ensuremath{\leqslant}0.5)$, specific heat measurements show a broad anomaly, suggestive of gross phase separation. We have performed x-ray absorption experiments at the $\mathrm{Ce}\phantom{\rule{0.3em}{0ex}}{L}_{\mathrm{III}},\mathrm{Ir}\phantom{\rule{0.3em}{0ex}}{L}_{\mathrm{III}}$, and $\mathrm{Rh}\phantom{\rule{0.3em}{0ex}}K$-edges as a function of Rh concentration and temperature. X-ray absorption near-edge structure measurements indicate that cerium is close to trivalent in this system, with no measurable change with temperature from 20--300 K, consistent with a heavy-fermion material. Extended x-ray absorption fine structure measurements as a function of temperature from all measured edges indicate the local crystal structure of all samples is well ordered, with no gross phase separation observed, even for samples with $x=0.125$ and $x=0.25$. These results therefore suggest that the anomalous specific heat behavior in the $0.1\ensuremath{\leqslant}x\ensuremath{\leqslant}0.5$ range have some other explanation, and some possibilities are discussed.

Specific heat of BaxSr1—xTiO3ferroelectric perovskites

The specific heat of an anharmonic BaxSr1—xTiO3 ferroelectric crystal is calculated in its paraelectric phase from the Silverman–Joseph Hamiltonian augmented with fourth order phonon coordinates using double time Green's functions. The soft mode contribution to specific heat is described by appropriate Einstein terms. The variation of specific heat with temperature and defect parameters is discussed. The effect of defects on specific heat can be observed in the presence of anharmonicity. Around the Curie temperature the Cochran soft mode is held to be responsible for the anomalous behaviour of specific heat.

Low-temperature thermal conductivity of ferroelastic Gd 2(MoO 4) 3

Thermal conductivity, k, of GMO crystal has been measured in temperatures from 0.5 to 80 K. The maximum of k appears at 18 K and its value depends on the current domain state of the sample. The ferroelastic domain walls and antiphase boundaries, characterised by elastic inhomogeneities, are responsible for additional phonon scattering and a decrease in the thermal conductivity. The deviation of the temperature dependence of thermal conductivity from the classical Debye theory observed below 4 K is related to the anomalous behaviour of specific heat in the region of the antiferromagnetic transition at T N =0.3 K .

Collapse transition of isolated Lennard-Jones chain molecules: Exact results for short chains

In this work we study flexible Lennard-Jones (LJ) interaction-site chain molecules with fixed bond length L. We obtain “exact” numerical results for the equilibrium configurational and energetic properties of LJ n-mer chains with n=3, 4, and 5 for a range of L (0.8⩽L/σ⩽21/6). These results include intramolecular site–site distribution functions and fluctuations in site–site distances, radius of gyration, and average potential energy. We also compute the single-chain specific heat, chemical potential, and theta temperature. With decreasing temperature the chain molecules undergo a collapse transition from an extended disordered state to a compact highly ordered state, exhibiting an associated peak in the specific heat. For n=3 and 4 the collapse occurs in a single stage whereas for the n=5 chains a multistage collapse is possible. In particular, the specific heat peaks associated with the collapse of 5-mer chains with bond lengths in the range 0.85⩽L/σ⩽1.0 display either a low temperature shoulder or secondary maximum. We show that this complex specific heat behavior arises when the initial collapsed state consists of a set of distinct and nondegenerate structural isomers. The secondary peak or shoulder is a result of the “freezing out” of all but the ground state isomer. These results are discussed in the context of the similar anomalous specific heat behavior, and low temperature structural transitions observed in recent simulation studies of square-well and LJ chains and atomic clusters.

Magnetic-field effects on two-Leg heisenberg antiferromagnetic ladders: thermodynamic properties

Using the recently developed transfer-matrix renormalization group method, we have studied the thermodynamic properties of two-leg antiferromagnetic ladders in a magnetic field. Based on different magnetization behaviors, we found a disordered spin liquid, the Luttinger liquid, spin-polarized phases, and a classical regime. Our calculations in the Luttinger liquid regime suggest that both the divergence of the NMR relaxation rate and the anomalous specific heat behavior observed on Cu2(C5H12N2)2Cl4 are due to a quasi-one-dimensional effect rather than three-dimensional ordering.

First order transitions by conduction calorimetry: Application to deuterated potassium dihydrogen phosphate ferroelastic crystal under uniaxial pressure

The specific heat c and the heat power W exchanged by a Deuterated Potassium Dihydrogen Phosphate ferroelectric-ferroelastic crystal have been measured simultaneously for both decreasing and increasing temperature at a low constant rate (0.06 K/h) between 175 and 240 K. The measurements were carried out under controlled uniaxial stresses of 0.3 and 4.5±0.1 bar applied to face (110). At Tt=207.9 K, a first order transition is produced with anomalous specific heat behavior in the interval where the transition heat appears. This anomalous behavior is explained in terms of the temperature variation of the heat power during the transition. During cooling, the transition occurs with coexistence of phases, while during heating it seems that metastable states are reached. Excluding data affected by the transition heat, the specific heat behavior agrees with the predictions of a 2-4-6 Landau potential in the range of 4–15 K below Tt while logarithmic behavior is obtained in the range from Tt to 1 K below Tt. Data obtained under 0.3 and 4.5 bar uniaxial stresses exhibit the same behavior.

Particle size and interfacial effect on the specific heat of nanocrystalline Fe

The specific heat of nanocrystalline iron with grain size of 40 nm has been measured in the low-temperature range from 1.8 to 26 K. The anomalous specific heat behavior of nanocrystalline iron is compared with that of the normal polycrystalline iron. It is found that the electronic specific heat coefficient γ obtained at low temperatures decreases by about 50%. A quadratic temperature-dependent term associated with surface modes in the heat capacity has been clearly observed. A large enhancement of the specific heat at higher temperatures is interpreted as the Einstein oscillator contribution due to weakly bound atoms at the interfaces of the nanocrystals.

Anomalous Specific Heat Behavior of Nanocrystalline Fe at Low Temperatures

The specific heat of nanocrystalline iron with grain size of 40 nm has been measured in the low temperature range from 1.8 to 26 K. The anomalous specific heat behavior of nanocrystalline iron is compared to that of the standard bulk iron. It is found that the electronic specific heat coefficient γ obtained at low temperatures decreases by about 50%. A T2 term in the heat capacity associated with surface modes has been clearly observed. A large enhancement of the specific heat at temperatures above 16 K may be interpreted as the Einstein oscillator contributions.

Study on the Order of the FR(LT)–FR(HT) Phase Transition of PZT Ceramics

By the experiments studying the FR(LT)–FR(HT) phase transition of PZT ceramics, it is reasonable to point out that the FR(HT) phase transition is of first order. The convincing experimental results show that during FR(LT)–FR(HT) transition, an anomalous behaviour of specific heat, abrupt volume change in thermal expansion, shift of phase transition temperature under dc bias, thermal hysteresis of pyroelectric current, and structural change from one space group to another take place.