Precise lattice parameter measurements in CsCl-Br solid solutions between room temperature and 90°K by powder x-ray diffraction

Solid solutions of CsCl-Br in five different concentrations were prepared in sealed quartz tubes by heating the mixture to 1123°K for 6–8 hr and quenching to room temperature. X-ray diffractograms were taken at eight different temperatures between room temperature and 90°K for these solid solutions using the YPC50NM powder diffractometer and a continuous flow cryostat. The observed lattice parameters for each sample at each temperature obtained from the powder diffractograms were then extrapolated to give the true lattice parameters using the least square method with Nelson-Riley extrapolation scheme. The values of the true lattice parameters at each concentration and at each temperature were tabulated and the results discussed. It is shown that the lattice parameters vs temperature for some concentrations exhibit an anomalous behaviour. Contribution No. 691     

Lattice parameter and thermal expansion of CsCl and CsBr by x-ray powder diffraction. II. Thermal expansion of CsBr from room temperature to 78.2 °K

The lattice parameters of CsBr at eight different temperatures from room temperature to 78.2 °K were measured and the true lattice parameters were obtained by the least squares method using the Nelson-Riley extrapolation function. Using these parameters the thermal expansion coefficients of CsBr were estimated at each temperature by fitting them into a cubic polynomial involving temperatureT. Theα _T thus obtained were compared with the values of earlier workers who used an interferometric technique and the agreement was found to be good.     

Spin squeezing and quantum correlations

We discuss the notion of spin squeezing considering two mutually exclusive classes of spin-s states, namely, oriented and non-oriented states. Our analysis shows that the oriented states are not squeezed while non-oriented states exhibit squeezing. We also present a new scheme for construction of spin-s states using 2s spinors oriented along different axes. Taking the case of s=1, we show that the ‘non-oriented’ nature and hence squeezing arise from the intrinsic quantum correlations that exist among the spinors in the coupled state.     

The second and third order elastic constants of alkali metals

The second and third order elastic constants of the alkali metals have been calculated on the long wave method using the Heine-Abarenkov lacal model potential with different exchange-correlation corrections. It is found that the use of an exchange correlation correction which satisfies the compressibility sum rule leads to a good agreement between the calculated and measured second order elastic constants of the alkali metals Na, K, Rb and Cs. The shear elastic constants however come out correct even if the compressibility sum rule is violated by the exchange-correlation correction. The third order elastic constants and the pressure derivatives of the second order elastic constants and the pressure derivatives of the second order elastic constants calculated on the HA local potential are lower than the experimental values at room temperature. The discrepancy is pronounced for the heavier alkali metals. Similar calculations using the Wallace potential for Li, Na and K and the Schneider-Stoll potential for Rb give the pressure derivative in good agreement with experiment. In view of the important role by the exchange correlation correction, Suzuki's results calculated without taking this correction into account can only be accepted with some reservation.     

Theory of sheath in a collisional multi-component plasma

The aim of this brief report is to study the behaviour of sheath structure in a multi-component plasma with dust-neutral collisions. The plasma consists of electrons, ions, micron size negatively charged dust particles and neutrals. The sheath-edge potential and sheath width are calculated for collisionally dominated sheath. Comparison of collisionless and collisionally dominated sheath are made.     

Temperature variation of the Debye-Waller factors of metal and halide ions in CsCl and CsBr powders by X-ray diffraction. II. Debye-Waller factors of Cs+ and Br− ions in CsBr from room temperature to 78.2°K

The temperature variation of the Debye-Waller factors of Cs⁺ and Br⁻ ions in CsBr powder has been studied using powder X-ray diffraction. The integrated intensities of the Bragg peaks at different temperatures have been obtained. These results have been verified by structure factor least squares refinement program. Theoretical shell model lattice dynamical calculations have been done using a 7-parameter model in the harmonic approximation and the values compared with the present X-ray measurements. The observed intensities have been corrected for first order thermal diffuse scattering.     

Analysis of a shielded TE011 mode composite dielectric resonator for stable frequency reference

Analysis of a TE₀₁₁ mode composite sapphire-rutile dielectric resonator has been carried out to study the temperature variation of resonance frequency, close to the Cs atomic clock hyperfine frequency of 9.192 GHz. The complementary behavior of dielectric permittivity with temperature of the composite has been exploited to obtain the desired turning point in the resonant frequency. The frequency of the composite structure is found to be independent of the shield diameter beyond four times the puck diameter.     

Temperature variation of the Debye-Waller factors of metal and halide ions in CsCl-Br solid solutions between room temperature and 90°K by powder X-ray diffraction

Solid solutions of CsCl-Br in different molal concentrations were prepared and X-ray diffractograms taken. The integrated intensities of the Bragg peaks have been estimated and structure factors were obtained. The crystal lattice in each of these solid solution samples is made up of a random distribution of Cs⁺, Cl^? and Br^? ions depending upon the molal concentration. A pseudo-atom model has been proposed in which the Cs⁺ ions occupy (000) position and a pseudo-atom occupies (1/2 1/2 1/2) position. The presence of incoherence scattering in these solid solutions has been considered by applying the necessary correction to the atomic scattering factors. The integrated intensities have been analysed and the temperature variation of the Debye-Waller factors of the metal (Cs⁺) ion and the pseudo ion (CB^?) have been estimated.     

Temperature variation of the Debye-Waller factors of metal and halide ions in CsCl and CsBr powders by X-ray diffraction. I. Debye-Waller factors of Cs+ and Cl− ions in CsCl from room temperature to 90°K

The temperature variation of the Debye-Waller factors of Cs⁺ and Cl⁻ ions in CsCl powder has been studied using X-ray powder diffraction. A continuous flow cryostat has been used to record the diffractograms and the integrated intensities of the Bragg peaks at different temperatures have been obtained. The integrated intensities of the odd and even reflections have been analysed following the structure of the CsCl compound and the Debye-Waller factors of the Cs⁺ and Cl⁻ ions have been estimated. The results have been verified by structure factor least squares refinement. Theoretical shell model lattice dynamical calculations have been done using a 7-parameter model in the harmonic approximation and the values compared with the present X-ray measurements.     

Temperature variation of the Debye-Waller factors of Ba++ and F− ions in BaF2 powder by x-ray diffraction

The temperature variation of the Debye-Waller factors of Ba⁺⁺ and F⁻ ions in BaF₂ powder has been studied using x-ray powder diffraction over the temperature range 77°–298°K. A continuous flow cryostat has been specially fabricated for this purpose for the YPC 50 NM powder diffractometer available in the department. The Debye-Waller factors of Ba⁺⁺ and F⁻ between room temperature and 879°K have been measured using single crystal neutron diffraction by Cooperet al. Theoretical lattice dynamics shell model calculations using a 7-parameter model in a quasiharmonic approximation have been done over a temperature range 77° to 879°K. The theoretical values have been compared with the present x-ray measurements and the single crystal neutron diffraction values and the results are discussed.