E. B. Amitin

Thermodynamic properties of dysprosium from 7 to 300 K

The heat capacity of high-purity dysprosium was measured over the temperature range 7 to 300 K by adiabatic calorimetry. Results of mass-spectroscopic and gas analyses as well as the ratio of resistivities R(300 K)R(4.2 K) ≈ 200 confirmed the high quality of the sample. Values of thermodynamic functions have been calculated: Cp(T), So(T), {Ho(T)−Ho(0)}, and −{Go(T)−Ho(0)}T at T = 298.15 K are respectively 27.73 J·K−1·mol−1, 75.55 J·K−1·mol−1, 8973 J·mol−1, and 45.45 J·K−1·mol−1. The phase transitions in dysprosium were found to be at 92.1 K and at 180.2 K. The influence of the purity of a sample on the thermodynamic functions is discussed.

Boundary line of the transition into the pseudogap state in thulium cuprates

Precision measurements of the heat capacity of 1-2-3 thulium cuprates with oxygen content ranging from 6.3 to 6.92 were performed in the temperature range 6–300 K. Analysis of the experimentl data showed anomalies in the temperature dependence of the electronic heat capacity. It is conjectured that the anomalies are due to a transition from the normal metallic into the pseudogap state.

Anomalies of the electronic heat capacity of thulium cuprates in the pseudogap phase region

Precision measurements of the heat capacity of thulium 1-2-3 cuprate with oxygen concentrations x=6.92 and x=6.7 are made in the temperature range 6–300 K. After the lattice components of the heat capacity of the samples are subtracted off, a comparison of the results makes it possible to determine the contribution to the heat capacity due to the formation of the pseudogap phase for the sample with x=6.7. The temperature dependence of this contribution has an anomaly near the boundary of the transition from the pseudogap phase to the normal metallic phase. The experimental results correlate with the theoretical ideas about the rearrangement of the electronic structure upon the transition of the system to the pseudogap phase region.

Heat capacity of NH4Cl1 − xBrx solid solutions in the vicinity of the γ-to-β phase transition

Abstract The heat capacities of the solid solutions NH 4 Cl 0.83 Br 0.17 , NH 4 Cl 0.75 Br 0.25 , NH 4 Cl 0.63 Br 0.37 , NH 4 Cl 0.50 Br 0.50 , and NH 4 Cl 0.20 Br 0.80 have been measured in a vacuum adiabatic microcalorimeter over the temperature range 200 to 300 K. Values of the molar capacity and enthalpy increment { H m o (300 K)− H m o (200 K)} of the solid solutions are compared with literature results. The behaviour of C an, m = ( C p , m − C reg, m ) near the order-disorder phase transition in these crystals has been analysed to obtain the critical exponent α in the γ-phase. The question of existence of tricritical points on the γ-to-β transition line is discussed. The effect of sample inhomogeneities on the character of C p , m is considered. The experimental molar heat capacities of NH 4 Cl 1 − x Br x are tabulated.

Thermal expansion anomalies in dysprosium

The temperature dependence of the thermal expansion coefficient along the hexagonal c axis of single-crystal dysprosium has been investigated in the vicinity of the phase transitions and near the temperatures where the periodicity of the helix spin structure is commensurate with that of the crystal lattice. No length discontinuity of more than 2*10-7 cm has been observed at the Neel temperature. On cooling the sample, a discontinuity in the relative length change of about Delta L/L=5*10-5 has been discovered at a temperature of about 171+or-1K. Its nature is attributed to a transition from a vortex structure to helical long-range order. At the Curie point the temperature and the magnitude of the length discontinuity depend on the thermal history of the sample. No anomalous changes in the thermal expansion coefficient have been observed at the temperatures where magnetic and crystalline structures are commensurate.

Thermodynamic properties of ammonium halogenides near their tricritical points

A study was made pertaining to anomalies of the specific heat of NH4,Cl and of NH4Cl1−xBrx solid solutions. It has been discovered that in addition to a classical tricritical behavior (α=0.5) there can also occur “Ising” anomalies (α 0.1) in the vicinity of tricritical points.

Scaling behavior in normal-state properties of underdoped TmBaCuO single crystals

Abstract Universal behavior of the in-plane resistivity is observed in the normal state of underdoped TmBa 2 Cu 3 O x single crystals. In the region 6.37 x ρ′(T, x), can be presented as a universal function of single dimensionless argument T / T *( x ). A single electron transport mechanism and a single energy scale in the investigated area of the phase diagram are necessary for the appearance of such scaling effect. In the low-temperature region the behavior of the universal curve is close to exponential ρ′=ρ max ′(A+B exp (−T*/T)). This fact may point to an important role of pseudogap or spin gap effects in transport properties of the cuprate systems.

Thermal expansion of dysprosium from 60 to 300 K

The thermal expansion coefficient α along the hexagonal c-axis of single-crystal dysprosium has been studied from 60 to 300 K. The measurements were made using a capacitance dilatometer with a resolution of 2 × 10−10 m. On cooling the sample from the paramagnetic phase,a discontinuity of ΔLL = 5 × 10−5 in the relative length change was observed at 171 K. No anomalies in α were found at temperatures where the magnetic and crystalline structures are commensurate.