Thermodynamic and magnetic properties of LaSn3

Thermal expansion coefficient between 77 and 900K, isothermal compressibility in the 0–80 Kbar pressure range, magnetic susceptibility between 77 and 1300 K and heat capacity at constant pressure in the 20–300 K temperature range were determined for the LaSn₃ compound. From the experimental data, the specific heat at constant volume was calculated and the thermal dependence of the Debye's parameter θ_D was obtained. The electron contribution to the heat capacity was also determined from the high temperature data. The magnetic properties confirm that there is no evidence of the existence of a magnetic moment localized on La atoms, in contrast with a previous report and in agreement with the general assumptions. A little anomaly found in the expansion coefficient, in the isothermal compressibility and in the specific heat is discussed in terms of a lattice order-disorder phenomenon.     

Phase transitions and thermal expansion in Ni<Subscript>51–<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>36 + <Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript>13</Subscript> alloys

Thermal expansion and structural and magnetic phase transitions in alloys of the Ni–Mn–Sn system have been investigated. The spontaneous martensitic transformation in Ni_51–xMn_{36 + x}Sn₁₃ (0 ≤ x ≤ 3) alloys is found to be accompanied by high jumps in the temperature dependences of the linear thermal expansion. The relative change in the linear sizes of these alloys at the martensitic transformation is ~1.5 × 10^–3. There are no anomalies in the magnetic-ordering temperature range in the temperature dependences of the coefficient of linear thermal expansion. The differences in the behavior of linear thermal expansion at the martensitic transformation in Ni_51–xMn_{36 + x}Sn₁₃ (0 ≤ x ≤ 3) and Ni₄₇Mn₄₀Sn₁₃(x = 4) alloys have been established.     

Thermal property of binary tetrahedral semiconductors

In this paper we present an expression relating the lattice thermal expansion coefficient α_L (10⁻⁶ K⁻¹) for the A^IIIB^V and A^IIB^VI semiconductors with the product of ionic charges (Z₁Z₂), melting temperature (T_m) and nearest neighbor distance d (Å). The lattice thermal expansion coefficient of these compounds exhibit a linear relationship when plotted on a log–log scale against the melting temperature (T_m), but fall on different straight lines according to the ionic charge product of the compounds. A good agreement has been found between the experimental and calculated values of the lattice thermal expansion coefficient for A^IIIB^V and A^IIB^VI semiconductors.     

Thermal and optical properties of diode side-pumped solid state laser rods

Thermal heating is a major limiting factor in scaling the average power of a solid-state laser. The relationship between the heat intensity in a laser slab and the heat transfer coefficient has been studied by considering the variations of thermal conductivity and expansion coefficient of the laser slab with temperature. In this paper, the laser rod has been studied by including its thermal, stress and optical aberration effects. It is pointed out that different heat transfer coefficients should be adopted according to different heat intensities inside the laser rod in order to obtain better pumping input as well as to optimize the cooling effects.     

Ablation of transparent solids during self-limited deposition of diamond-like films from liquid hydrocarbons

A novel effect is studied of self-limitation of the diamond-like film thickness during laser irradiation of the interface of transparent substrates with liquid aromatic hydrocarbons. The interface is exposed through the transparent substrate to radiation of a copper vapor laser (wavelength of 510.6 nm, pulse duration of 20 ns). The thickness of diamond-like film increases linearly to 80-100 nm with the number of laser pulses and then saturates, while the substrate is ablated with nearly constant rate. This ablation rate depends on the thermal expansion coefficient of the substrate (glass, fused silica, sapphire, or CaF₂). The absorption of extinction coefficient of deposited films measured by ellipsometry is of order of 10⁴ cm^-1 and is sufficient to cause the significant heating of the interface. The ablation of the transparent substrates is due to their unequal thermal expansion compared to the diamond-like film having different thermal expansion coefficient. The measured ablation rates scale from 0.2 Å/pulse for glass to 4.5 Å/pulse for CaF₂. A 7m spatial resolution of the ablation process has been demonstrated for fused silica.     

Design of an optical fiber sensor for linear thermal expansion measurement

Design and operation of an optical fiber device for temperature sensing and thermal expansion measurement are reported. The modulated intensity has been measured by using a pair of 450 μm core fiber, one acting as the source and the other one as receiving fiber. In this design, the light intensity modulation is based on the relative motion of the optical fibers and a reflective coated lens. By using displacement calibration data for this sensor, the linear thermal expansion of the aluminum rod is determined. This sensor shows an average sensitivity of about 11.3 mV/°C for temperature detection and 7 μm/°C for thermal expansion detection. Device resolution for a linear expansion measurement is about 3 μm for a dynamic range of 600 μm corresponding to a temperature change of 100°C. The measured linear expansion results are checked against the expected theoretical ones and an agreement within ±2 μm is noticed. The operation of this sensor was also compared with other types and some advantages are observed, which verify the capability of this design for such precise measurements.     

Lattice properties in the vicinity of the martensitic transformation in TiNi

A pronounced peak in the thermal expansion coefficient — and thus in the Grüneisen parameter — has been found at the temperature corresponding to the martensitic transformation in TiNi. This finding, together with results of ultrasound wave propagation studies, attests to anomalous lattice-dynamical behaviour in the vicinity of the phase transition. Ultrasonic wave attenuation and velocity data are interpreted on the basis of Akhieser-type, phonon viscosity damping. Results obtained are consistent with the hypothesis that a soft phonon mode plays a dominant role in the lattice properties of TiNi near the transition.     

Mechanical stability and thermodynamic properties of OsC from first-principles calculations

The elastic and thermodynamic characteristics of OsC crystal have been predicted through a method of density functional theory within the generalized gradient approximation (GGA). Compared with WC-type OsC, NaCl-type OsC is not only energy unfavorable but also mechanics unstable. The five independent elastic constants (C_ij), bulk modulus (B₀), the dependence of bulk modulus on temperature and pressure as well as the thermal expansion coefficient (α_V) at various temperatures for WC-type OsC are discussed. According to our calculations, WC-type OsC should be an ultra-incompressible material with high bulk modulus about 381 GPa. In addition, the bulk modulus will increase with increasing pressure while decrease with increasing temperature. The researches on the thermal expansion coefficient indicate that there will be a knee point during the process of thermal expansion coefficient variation versus increasing temperature. Our results may provide useful information for theoretical and experimental investigation of OsC.     

Lattice dynamics,third order elastic constants and thermal expansion of rhenium

A systematic investigation of the lattice dynamics, second and third order elastic constants and thermal expansion has been carried out in rhenium using Keating's approach. The ten third-order elastic constants of rhenium are calculated using four anharmonic parameters. The present model reproduces the measured pressure derivatives of the second order elastic constants well. The low and high temperature limits γ&#x0304;L and γ&#x0304;H of the lattice thermal expansion are calculated. The agreement between the calculated γ&#x0304;H and that obtained by Gschneidner from the thermal expansion and specific heat data of rhenium is satisfactory.     

金属和玻璃胶合体热膨胀仿真及实验验证

仿真分析了热膨胀系数不同的金属和玻璃胶合体在不同温度下的形变,同时使用热膨胀仪测试了不同金属的热膨胀系数,随后,将热膨胀系数不同的金属分别与相同材料的玻璃进行胶合,最后将胶合体置于半封闭空间并对其整体进行加热,采用哈特曼波前测试系统测试胶合体的形变。结果表明,胶合体的仿真数据和实验数据基本吻合。该仿真与实验结果,对不同材料属性的胶合体在热膨胀匹配设计方面具有一定的指导意义。     

Thermal expansion behavior of silicon at low temperatures

Lattice parameters, thermal expansion coefficients and Grüneisen parameters of silicon are determined by an X-Ray diffraction method in the temperature range of 180–40 K without the use of liquid gases. Thermal expansion of silicon becomes negative below 120 K which is discussed in terms of its lattice vibrations and crystal structure.     

Temperature dependent LEED study of Pb{1 1 1}

The thermal behavior of Pb{1 1 1} was studied using low-energy electron diffraction (LEED) in the temperature range 11–323 K. The surface interlayer spacings increase with temperature at about the same rate as the bulk up to 0.5 T_m, and then increase faster. The relaxation of the surface, which is larger than for other fcc {1 1 1} surfaces, is maintained in the temperature range studied. Although Pb has a larger expansion coefficient than other metals, the surface thermal expansion behavior is in line with other surfaces, and is consistent with harmonic interplanar potentials.     

Temperature dependence of thermal expansion coefficient of crystals with cubic syngony

A simple analytic temperature relationship for the thermal expansion coefficient of crystals with cubic syngony was obtained, and the thermal expansion coefficients of some crystals of this class were determined experimentally; the results agreed satisfactorily with the curve obtained from formulas (5) and (6). The temperature range from liquid nitrogen up to temperatures around 1000 ° K was investigated, and the results were compared with data given by other authors.     

Measurement of the thermal expansion coefficients of ferroelectric crystals by a moiré interferometer

A moiré interferometer is used to measure the thermal expansion of two ferroelectric crystals, LiNbO₃ and KTiOPO₄. The crystal samples are patterned with a chromium reflective grating and used as a diffractive component in a reflective grating interferometer. The thermal expansion of all the three axes of congruent LiNbO₃ and of x and y axes of the flux-grown KTiOPO₄ were measured from room temperature to 200 °C. For this temperature range the thermal expansion coefficient has been modeled by a second-order polynomial and its coefficients have been estimated by accurate analysis of the resulting moiré fringe pattern.     

Thermal properties of PCR-1 and PCR-37 piezoceramics

The temperature dependences of the thermal conductivity (300–800 K), specific heat, and thermal expansion coefficient of PCR-1 and PCR-37 piezoceramics have been experimentally determined. Anomalies are found near the Curie temperature, which are caused by changes in the phase composition variations and structure rearrangement.     

Heat capacity anomaly in UO2 in the vicinity of 1300 K: an improved description based on high resolution X-ray and neutron powder diffraction studies

X-ray and neutron powder diffraction studies of UO₂ were performed under controlled oxygen partial pressure between room temperature and 1673 K. More than 40 neutron diffraction patterns were recorded. The thermal expansion coefficient of UO₂ and the temperature dependence of Debye-Waller factors for oxygen and uranium atoms were determined. The dependence of Debye-Waller factors as a function of temperature is linear and the thermal expansion coefficient follows the classical Debye regime within the temperature range 300-1000 K. Above 1200 K, a departure from this quasi-harmonic behavior is clearly observed. Both an abnormal increase of the thermal expansion and of the oxygen sublattice disorder are evidenced. The departure of the lattice parameter from a linear thermal variation is found to be thermally activated with an effective activation energy close to 1 eV, very similar to the activation energy already found for the electrical conductivity. This new result suggests that polarons may affect the mean lattice parameter. A new thermodynamic model is then proposed to explain the heat capacity thermal variation by only three contributions: harmonic phonons, thermal expansion and polarons.     

兔主动脉冻结膨胀行为及其影响因素的研究

文采用热机械分析仪(TMA)分别研究了低温保护剂(CPA)和冻结速率对兔主动脉冻结相变过程中膨胀的影响。研究结果表明:在兔主动脉的冻结过程中,先是逐渐膨胀到某一峰值,然后突然有收缩的发生;降温速率越大,其相应的热膨胀系数也越大;添加二甲亚砜(DMSO)大大增加了主动脉冻结过程的未冻水含量,从而对其冻结膨胀有明显影响,而且,DMSO浓度越大,其冻结膨胀系数越小。     

Heat transfer for diode side-pumped YAG slabs

Thermal heating is a major limiting factor in scaling the average power of a solid-state laser. The heat transfer coefficient is affected by the coolant flow rate, the physical properties of the laser slab and the coolant, and the pumping cavity geometry. The relationship between the heating effects and the heat transfer coefficient has been studied by considering the variations of thermal conductivity and expansion coefficient of the laser slab with temperature. It is concluded that different heat transfer coefficients should be adopted according to different heat intensities inside the laser slabs in order to obtain better pumping input as well as to optimize the cooling effects.     

Thermal expansion coefficient of alumina films developed by oxidation of a FeCrAl alloy determined by a deflection technique

Thermal expansion coefficients of α alumina films formed by oxidation of an oxide dispersion strengthened (ODS) FeCrAl alloy have been determined between 20 and 900 °C using an original deflection test. This technique is based on the curvature of a dissymmetrical sample consisting of a thin and elongated metallic substrate covered on one of its large sides by an oxide film. The average value of the expansion coefficient of the compact columnar α alumina film is found to equal 10.3 × 10⁻⁶ K⁻¹ which is higher than most values given in the literature.     

Thermal expansion of La3S4 at low temperatures

The thermal expansion of the superconductor La₃S₄ has been investigated on a single crystal by a capacitive method between 1.6 and 14 K. The relative length change shows a well pronounced second order phase transformation near 8.05 K, which is caused by the superconducting transition. From the calculated linear thermal expansion coefficient we determine the pressure coefficient of the transition temperature and of the thermodynamic critical field as well as the thermodynamic critical field itself. Furthermore we estimate the electronic, phononic and total Grüneisen parameters. These parameters have been used to discuss on the basis of the McMillan equation the reason for the increase of the transition temperature under pressure.