The phase boundary of the binary liquid system CS₂+CH₃NO₂ is studied over nearly six decades in reduced temperature 3×10⁻⁶<ε=(T_C−T)/T_C<2×10⁻¹ and over the composition range 8-98 mole % of CS₂. The critical parameters areT_C=335.13₂K andx_C=57.3₄ mole % of CS₂. A single critical exponentβ=0.315±0.004 fits the observations over the entire range with no indication ofβ increasing to the classical value of 1/2 far away fromT_C. The diameter of the coexistence curve shows a rectilinear behaviour only far away fromT_C. NearT_C, the deviation ΔX from the rectilinear law seems to fit a curve of the form ΔX=fε^7/8 exp (−gε^h), the derivative of which has a singularity like that of specific heat. An ambiguity in the analysis of the data in terms of mole fractions and volume fractions is pointed out. It is also suggested that the curvature of the diameter may be much weaker in a liquid-gas system and hence might have escaped detection.

The cylindrical approximation originally proposed by Pippard for the λ-transitions in one-component systems is extended to multicomponent systems. The application of the generalised Pippard relations to binary liquid mixtures is considered. The relations for He³ + He⁴ mixtures are shown to be equivalent to those obtained by earlier workers. The validity of the relation relating specific heat and thermal expansion for binary liquid systems is discussed on the basis of the measurements performed on the system methaonl +n-heptane. Lack of information on the behaviour of a few quantities prevents a quantitative test of the relation.

The elastic constantsC₁₁,C₁₂ andC₄₄ of sodium chlorate single crystal have been evaluated using 10 MHz ultrasonic pulse echo superposition technique. The values areC₁₁=4.90,C₁₂=1.39,C₄₄=1.17 (× 10¹⁰N/m²) at 298 K and 6.15, 2.16, 1.32 (×10¹⁰N/m²) at 77 K. The data agree well with the values measured earlier up to 223 K. Brief mention is also made of the low temperature bonding problems in these soft crystals.

The elastic constantsC₁₁,C₁₂ andC₄₄ of sodium bromate single crystals have been evaluated using 10 MHz ultrasonic pulse echo superposition technique. The values areC₁₁=5.57₈,C₁₂=1.07₅,C₄₄=1.51₀ (×10¹⁰ N/m²) at 290 K and 6.35, 1.98 and 1.65 (×10¹⁰ N/m²) at 77 K. The present room temperature values agree closely with the recent values of Gluyaset al. but the other earlier measurements show some scatter. A comparison between the elastic constants of sodium bromate and sodium chlorate is also made.

Electrical resistance measurements are reported on the binary liquid mixtures CS₂ + CH₃CN and CS₂ + CH₃NO₂ with special reference to the critical region. Impurity conduction seems to be the dominant mechanism for charge transport. For the liquid mixture filled at the critical composition, the resistance of the system aboveT_c follows the relationR=R_c−A(T−T_c)^b withb=0·6±0·1. BelowT_c the conductivities of the two phases obey a relation σ₂−σ₁=B(T_c−T)^β with β=0·34±0·02, the exponent of the transport coefficient being the same as the exponent of the order parameter, an equilibrium property.

A fully automated calorimeter has been designed and tested over the temperature range 200K–400K. The system may be used for measurements with an absolute accuracy of 0.2% of samples of approximate mass 50g and thermal capacity 15 JK⁻¹. The temperature of the sample is determined by a quartz crystal thermometer of resolution 100 µK which is not in direct thermal contact with the sample. The performance of the system is illustrated by results obtained on high purity copper, distilled water and K₂PbCu(NO₂)₆ which exhibits very sharp first order phase transitions at about 273.4K and 281.8K.

The electrical resistance of the binary liquid system cyclohexane + acetic anhydride is measured, in the critical region, both in the pure mixture and when the mixture is doped with small amounts (≈ 100 ppm) of H₂O/D₂O impurities.T_c was approached to aboutt=3×10⁻⁶ wheret=(T −T_c)/T_c. The critical exponentb ≈ 0.35 in the fit of the resistance data to the equationdR/dT ∼t^−b does not seem to be affected appreciably by the impurities. There is a sign reversal ofdR/dt in the non-critical region. Binary liquid systems seem to violate the universality of the critical resistivity.

The design and construction of precision temperature controllers, capable of tracking the temperature of the samples to within 1 mK for ramp heating rates from 0.05 to 10 K per hour, are discussed. A tutorial section on the evolution of the control loop configuration is first given. This is followed by an outline of the refinements of the basic control loop desirable in the actual implementation of the electronic controller. The novel features of the present system and its performance are then briefly discussed. Finally the inadequacy of the conventional PID controllers for this application, the estimation of the time constants of the physical system needed in the design of the electronic controllers and the pitfalls in using a simple model of the heater plus thermometer assembly with a single pole are also discussed.

The elastic constants of single crystal galena have been determined from the measured ultrasonic velocities down to liquid helium temperature. A cryostat incorporating an arrangement to inject the liquid bonding material at low temperature is described. At 5 K, the values of elastic constants are C₁₁=14.9₀, C₁₂=3.5₁ and C₄₄=2.9₂×10¹⁰ N/m².

Precise measurements of 10 MHz frequency longitudinal and shear wave velocities are reported in amorphous SeGe alloys near their glass transition temperature T_g. There is a sharp decrease of the velocities near T_g, but the reduction in velocities appears smaller than expected.

The electrical resistanceR and the dieletric constant э of the critical binary liquid mixture methanol plus cyclohexane has been measured near the critical point at five different spot frequencies from 10–100 kHz. The data are analysed using a nonlinear least squares routine. The fit is equally good for ana (=0·1) divergence or a 1 −v (=0·35) divergence of dR/dT and dэ/dT. Additional reasons are advanced to indicate that thea divergence is a better description.

The effect of gravity on various thermodynamic properties near the gas-liquid critical point has been calculated. Using a simple equation satisfying scaling requirements, an analytic expression for density profile is obtained, using which the effect on different thermodynamic properties can be easily calculated.

The electrical resistivity of bulk Ge₂₀Te₈₀ has been measured as a function of pressure and temperature. At 5 GPa, an amorphous semiconductor-to-crystalline metal transition has been observed. The sample recovered from the high pressure cell, after the application of 7 GPa, has a face-centred cubic structure with a lattice constant of 6·42 A. In crystalline sample, the semiconductor-to-metal transition occurs at 7 GPa. The thermoelectric power has also been measured for glassy samples in the temperature range 300–240 K.

The pressure dependence of the electrical resistivity of bulk GeSe₂ glass shows a semiconductor-to-metal transition at 7 GPa pressure. The high pressure phase is examined using the x-ray diffractometer and is found to be crystalline, with a face-centred cubic structure havinga = 4·06 A. The electrical conductivity has also been studied as a function of temperature at various pressures.

Electron and x-ray diffraction experiments on the metlt-spun Al_100−xFe_x (x=14, 18, 25) alloys are carried out. It is observed that all the melt-spun alloys possessing the quasi-crystalline phases have icosahedral point-group symmetry.

The electrical capacitance of the binary liquid mixturen. heptane + methanol at its critical composition is studied in both one-phase and two-phase regions. The two-phase capacitance data are used with the known functional forms for the order parameter and the diameter to obtainT_c andc_c with greater precision. This helps in reducing the number of unknown parameters in the functional form for the one-phase capacitance. The data show consistency with an alpha (α) exponent for dc/dt in the one phase region.

The article reviews the experimental techniques used in high pressure-low temperature investigations to study a variety of physico-chemical phenomena. The general principles of producing high pressures at low temperatures, the methods of measuring P and T, the materials used for construction and the diamond anvil cell (DAC) are briefly given first. Specific pieces of apparatus to measure the mechanical properties, phase equilibria, thermal properties, electrical properties, magnetic phenomena, optical and Raman/IR spectroscopic behaviour as well as Mössbauer spectra are then discussed. While instrumentation is the main emphasis of the article, a few illustrative examples of interesting observations are also indicated. Over 250 current papers are cited.

The ternary glasses of arsenic and germanium with antimony and selenium can be prepared in large sizes for optical purposes. The elastic behaviour of eight compositions of each glass has been studied down to 4.2 K using a 10 MHz ultrasonic pulse echo interferometer. The glasses have a normal elastic behaviour, with the velocities gradually increasing as the temperature is lowered. An anharmonic solid model of Lakkad satisfactorily explains the temperature variations. The elastic moduli of Ge_xSb₁₀Se_90−x glasses increase linearly as the Ge content is increased up to 25 at. % and beyond this the increase is nonlinear. (AsSb)₄₀Se₆₀ glasses show a linear increase in elastic moduli with increasing Sb content. The elastic moduli of As_xSb₁₅Se_85−x glasses exhibit a drastic change near the stoichiometric composition As₂₅Sb₁₅Se₆₀. These behaviours have been qualitatively explained on the basis of the structural changes in glasses.

The two dimensional plane can be filled with rhombuses, so as to generate non-periodic tilings with 4, 6, 8, 10 and 12-fold symmetries. Some representative tilings constructed using the rule of inflation are shown. The numerically computed diffraction patterns for the corresponding tilings are also shown to facilitate a comparison with possible X-ray or electron diffraction pictures.

The diffraction patterns from Fibonacci quasilattices have been calculated. Finite-size effects are evaluated for weak and strong peaks. For a smaller number of scatterers (<100) there are fluctuations in the intensities of weak and strong peaks. The fluctuations in weak peaks are greater than that in strong peaks. The fluctuations in intensities of weak and strong peaks near the origin are larger than in the corresponding cases of weak and strong peaks far away from the origin. Small shifts in peak-positions are unexpectedly found, the shifts being proportional toN^−3/2 for a large number of scatterers. The diffraction pattern of a one-dimensional crystal and random structure is compared with that of the Fibonacci quasilattice. The strong peaks observed in the diffraction pattern of 1-d crystal show negligible peak-shifts, they being comparable with computational errors even when the number of scatterers is as small as 5. The implications for analysing the experiments are briefly indicated.

A method for generating aperiodic tilings with five fold symmetry is discussed here. Basic patterns formed within decagons can be used to fill two dimensional space, by matching such suitable patterns. It appears to be possible to generate perfect tilings without retracing already established coordinates imposing conditions at the initial stages of generating them. Various possible ways to generate tilings, when perfectness is not required, are discussed. The calculated diffraction patterns for some representative finite size tilings are shown. There are subtle differences in the intensities of peaks in the diffraction patterns corresponding to different finite size tilings constructed using intersecting decagons. These effects persist for a larger number of scatterers in weak peaks than in strong peaks. They are unaffected by an introduction of systematic disorder. These effects could be termed as the finite size boundary effects. There are also small shifts in the peak positions owing to the finite size effects. The possibility of formation of large approximate square cells in large tilings is shown.

We report here a systematic data analysis of the vapour pressure of argon at different amounts of the liquid phase to understand the thermodynamic behaviour of this inert gas around triple point. At the triple point plateau, the applied heat pulse melts a certain phase of solid argon into liquid and increases vapour pressure. It is observed that this vapour pressure attains the thermodynamic equilibrium pressure after a certain time interval. The expoential decay of the vapour pressure as a function of time at different fractions of the liquid phase shows two different features. In one region, the relexation time constant (τ) is low and is not varying with the liquid phase, while in the other region the value ofτ increases with the amount of the liquid phase. Further, the peak pressure from the equilibrium pressure (ΔP_h), obtained from the fitting parameters, shows a dip at around 50% of the liquid phase. A qualitative physical interpretation has been given to explain these results.