Conductivity of C60 fullerene crystals under dynamic compression up to 200 kbar

The conductivity σ of C₆₀ fullerene crystals is measured under quasi-isentropic loading by a spread shock wave to a pressure of 200 kbar at the initial temperatures 293 and 77 K. A sharp increase in σ by seven to eight orders of magnitude is detected: from 10^?6?10^?7 Ω^?1 cm^?1 at normal conditions to 5 Ω^?1 cm^?1 under pressure from 100 to 200 kbar. The conductivity of samples under pressure decreases with decreasing temperature, which is characteristic of semiconductors. On pressure release, σ regains its initial value.     

Compression of lanthanum to 120 kbar

Lanthanum is studied by high pressure X-ray diffraction. The equation of state of the f.c.c. phase is determined at room temperature up to 120 kbar. The variation of the bulk modulus is compared with respective data of other rare earth elements.     

Melting temperature of lead and sodium at high pressures

We have redetermined the melting temperature of lead and sodium as a function of pressure in a new pressure cell made up of low strength materials. Many of the anomalies reported in a prior determination of the melting curve of lead have largely disappeared. The slope of our new melting curve for lead is in close agreement with the slope computed from thermochemical data.One new curve for sodium differs only slightly from the prior published curves.     

Compression and polymorphism of potassium to 400 kbar

Both the compression and polymorphism of K were investigated to about 400 kbar at room temperature in a diamond-anvil pressure cell by optical and X-ray diffraction techniques. The ambient b.c.c.-K(I) is stable to about 120 kbar. The compression data for K(I), fitted to the Birch equation of state, yielded the zero-pressure bulk modulus B₀ = 29.9 ± 0.2 kbar and its first pressure derivative B'₀ = 4.15 ± 0.10. These values agree very well with those of recent data derived from the direct measurement of length changes using piston-displacement (to 20 kbar) and laser interferometer (to 7 kbar) techniques. On the basis of the compression data for K(I) alone, Bridgman's pressure scale may be overestimated by about 10 kbar at 100 kbar and that of Kennedy and LaMori may be underestimated by about 5 kbar at 50 kbar. Two high-pressure polymorphs of K were revealed in the pressure range 100–200 kbar. The b.c.c. → f.c.c. transition in K was observed to occur near 120 kbar, accompanied by a −2.5% discontinuous change in volume. The sample changes gradually from silver to gold in the range 130–150 kbar. The f.c.c.-K.(II) transforms further into an as yet undetermined structure between 170 and 190 kbar. No change in colour was observed in the latter transition. K(III) is stable up to at least about 400 kbar. The equation of state for the f.c.c. phase of K cannot be established. The volume of K was compressed more than 60% in the vicinity of 200 kbar, however.     

Compressibility of hexagonal selenium to 45 kbar

Compression data to 45 kbar have been obtained for hexagonal selenium by static methods in a piston-cylinder apparatus. Cylindrical samples (1 cm dia. and 1·2 cm length) of polycrystalline hexagonal selenium, with a bulk density close to the X-ray density, were prepared by pressing the samples at 7 kbar and 170°C. The compression data are described by a third degree polynomial,

$?\left(\frac{\Delta V}{V_O}\right)=?64·14\times {10}^{?4}P+109·9\times {10}^{?6}{P}^2?96·77\times {10}^{?8}{P}^3$

,where P is pressure in kbar. The zero pressure bulk modulus and the pressure derivative of the bulk modulus are 156 ± 10 kbar and 4·33 respectively.     

Thermal conductivity of KCl up to 19 kbar

The pressure dependency of the thermal conductivity of KCl has been measured at room temperature up to 19kbar. The high pressure tool was of the “belt” type and a solid medium was used. The specimen was cylindrical and was heated along its axis. The conductivity was found to increase linearly at a rate of (3·3 ± 0·3) per cent/kbar.     

Raman spectroscopy of solid nitrogen up to 374 kbar

We measured the Raman spectrum of room-temperature solid nitrogen in a diamond cell at pressures up to 374 kbar. Only the molecular stretching mode was observed. The frequency of this mode appears to increase smoothly from 2340 cm^-1 at 39 kbar to 2394 cm^-1 at 374 kbar. Between about 50 and 120 kbar, the Raman line is split into a second, higher-frequency peak, which may be associated with molecular ordering in the solid. Measurements of broadening and splitting in fluorescence lines from the ruby pressure gauge indicate that solid nitrogen is reasonably plastic up to 130 kbar. We suggest that nitrogen might serve as a useful pressure medium.     

Electric-field-induced phase transition in single-crystal lead zinc niobate

The behavior of lead zinc niobate, a relaxor ferroelectric, in electric fields has been studied by dielectric, optical transmittance, and small-angle light scattering techniques. A field-induced transition from an averaged cubic to macrodomain ferroelectric phase has been found. A comparison is made with the properties of the phase induced in lead magnoniobate, a classical relaxor. Fiz. Tverd. Tela (St. Petersburg) 40, 527–530 (March 1998)     

Optical characterization of Cu ion-doped zinc lead borate glasses

We have developed a new series of zinc lead borate (ZLB) glasses by varying ZnO content, to enhance UV transmission, in the chemical composition of xZnO-15PbO-(85−x)B₂O₃, where x=0, 5, 10, 15, 20, 25, 30, 35, 40 and 45 mol% ZnO. From the measurement of UV absorption spectra both the direct and indirect band gaps have been evaluated. Also different physical properties of a reference glass of 45ZnO-15PbO-40B₂O₃ have been studied. From the measurement of refractive indices at six different wavelengths, Cauchy's constants (A=1.578743209; and ) have been computed and a satisfactory correlation has been achieved between the theoretical and the experimental results. Absorption spectra of Cu²⁺(45−x)ZnO-15PbO-40B₂O₃ (where x=0.1, 0.2, 0.5 and 1.0 mol%) have shown two absorption bands at 428 nm (²B_1g→²E_g) and 777 nm (²B_1g→²B_2g). Emission spectra of (1.0 mol%) Cu²⁺:ZLB have revealed two emission transitions at 400 and 493 nm with excitations at 288 and 316 nm.     

First and second order Raman scattering in GaP to 128 kbar

One- and two-phonon room temperature Raman spectra of GaP were measured to 128 kbar using a diamond-anvil pressure cell. Linear and quadratic pressure coefficients were determined for phonons at Γ, L, (X→K), and Σ. The results suggest possible “soft” mode behavior for TA(L) and TA(X→K) phonons.     

Insulator-metal transitions and superconductivity of amorphous semiconductors at pressures up to 250 kbar

Abstract

The problem of the insulator-metal (I-M) transition in amorphous substances has recently become the subject of a great interest. Of particular interest is the behaviour of such systems near the I-M transition. We shall consider the And erson I-M transition which takes place when the Fermi level EF crosses the mobility threshold E, as some outer parameter is changed.     

The pressure dependence of elastic moduli of NiF2 to 10 kbar

At room temperature, the pressure dependence of the elastic stiffness moduli of NiF₂ have been measured by pulse superposition method to 10 kbar. The observed strong decreasing behavior in the modulus $\text{C}{}_{\mathrm{<mtext>s</mtext>}}\text{=}\text{1}\text{2}\text{(C}{}_{11}\text{? C}{}_{12}\text{)}$ is discussed.     

铌锌酸铅-钛酸铅薄层中Lamb波模式的交叉特性

以[001]_c和[011]_c极化的铌锌酸铅-钛酸铅晶体为研究对象, 利用子波理论对其无限大自由薄层中传播的Lamb波的色散及模式交叉特性进行了研究. 发现只有[001]_c极化的晶体中的对称与反对称模式Lamb波之间出现了多次交叉, 并且变化规律与铌镁酸铅-钛酸铅的情形相同. Lamb波的A₀和S₀模式的交叉是由准纵向剪切波慢度曲线的多值关系引起的, 此时其x₃方向的波数在一定范围内存在一对非纯虚数的复共轭根. 利用此结论推导出A₀和S₀模式交叉时弹性常数需要满足的条件, 为判断正交、四方对称性晶体中Lamb波的A₀和S₀模式是否交叉提供了一种直观、简便的方法.     

A new hydrostatic medium for diamond anvil cells to 300 kbar pressure

We have shown that the rare gas xenon provides a hydrostatic medium for gasketed samples in a diamond anvil cell to pressures of 300 kbar. Previously, hydrostatic conditions were limited to ～100 kbar in a methanol-ethanol mixture. Three spectroscopic tests were used to determine that pressure gradients were small in the solidified gas. Since xenon has a convenient melting temperature, easy cell loading is possible. The small volume in the gasket requires only a few cm³ of gas. By analogy the other rare gases may be expected to show similar hydrostatic properties. Helium, for example, would be useful for X-ray studies.     

Equation of state of sodium chloride up to 32 kbar and 500°C2

The length change of a 25mm long single crystal of NaCl has been determined as a function of hydrostatic pressure up to 32 kbar and temperatures up to 500°C using an electrical contact piezometer with tungsten carbide as a standard. The measurements were carried out in an end loaded piston cylinder apparatus. The length change of the tungsten carbide standard is small compared to that of NaCl and therefore reliable data are obtained. Compression data by Bridgman[1] and thermal expansion data by Kennametal Inc. were used for the equation of state of tungsten carbide. We estimated an absolute uncertainty in the length change measurement of NaCl of ±0.7%. The temperature was accurate within 0.3°C. The uncertainty in pressure is ±0.4%. The results are compared with Decker's [2] equation of state which is frequently used when NaCl is taken as a standard in high pressure work. At room temperature we find a smaller compression of NaCl than Decker and find excellent agreement with Bridgman's[3] data. At higher temperatures we find very good agreement between our data and Decker's equation of state.     

Analysis of Melting Particle Model and Microwave and MM-Wave Scatterings Due to a Melting Layer of Precipitation

In this paper, the water-coated snow sphere model of melting particles has been given. Based on this model, the scattering properties and albedo w₀ of melting particles have been calculated by use of the coated sphere BHCOAT method. It is shown that the albedo of melting particles may be more than the raindrops and snow spheres at 5 (C-band) and 14GHz (Ku-band). The albedo of melting particles are nearly less than the equivalent mass raindrops albedo at the Ka and mm-band of f > 20GHz. These results are in agreement with the conclusion radar observed and literature given^[1,2]. It demonstrates that the water-coated snow sphere model of melting particles is appropriate and practicable. The study is significant for the utilization of the low fade margin system in satellite communication.