Variation of the piezo-electric constants of α-quartz with temperature

The method of finding the piezo-electric constants with the help of the variations of bond distances and bond angles on strain has been utilised in finding the variations of the piezo-electric constants ε₁₁ and ε₄₁ of α-quartz with temperature. It is found that the variations of ε₁₁ with temperature can be explained on the basis of the change of co-ordinates with temperature. At 558° C. the silicon atoms are found to occupy the same positions as they do in β-quartz. As the transition temperature is reached, the longitudinal coefficient ε₁₁ drops to zero, while the transverse coefficient ε₄₁ decreases by only 15%. The piezo-electric constant of β-quartz has been similarly determined and its value comes out to be 1·05×10⁴ for a non-ionic crystal (k=·724) and 1·45×10⁴ for an ionic crystal (k=1).     

Acoustic levitation and its application in estimation of high power sound field

Acoustic levitation has been studied using airborne radiation from a high power magnetostrictive ferrite transducer of frequency 18 kHz. Spherical solid objects as well as liquid drops of varying weight and radii have been levitated under I G at the velocity antinodes of the standing waves formed with the help of a reflector. The dependence of the maximum weight of a spherical object that can be levitated on the sound pressure level and the radius of the obstacle has been studied. An attempt has been made to estimate the radiated high power sound intensity from the maximum weight of the spherical object that can be levitated.     

Cathodo-luminescence spectra of alkali halides

Cathodo-luminescence spectra of fourteen alkali halides and of some mixed crystals of NaCl and KCl have been studied. The spectra show broad structureless bands. In some ten halides it is possible to find a strong band whose peak position shifts towards longer wavelengths as the inter-atomic distance increases. For pottasium halides the relationship λ_max=1380d, where “d” is the inter-atomic distance, holds approximately but is not generally true. A mechanism of cathodo-luminescence in alkali halides has been postulated, and an interpretation of the above band and of some NaCl bands has been made on that basis.     

Isotope shifts and electronic configurations of some of the energy levels of the neutral gadolinium atom

Isotope shift ΔT (156–160) have been evaluated for 52 odd and 90 even energy levels of the neutral gadolinium atom from the measurements carried out on 166 lines of the first spectrum in the region 4535–4975 Å on a photoelectric recording Fabry-Perot Spectrometer and enriched samples of ¹⁵⁶Gd and ¹⁶⁰Gd. Earlier studies provide data for just two lines in this region. Assignment of electronic configurations to some of the energy levels have been either confirmed or revised; some unassigned levels have been assigned probable configurations. The present study provides, for the first time, isotope shift of the two levels of 4f⁷6s²7 s configuration of Gd I.     

Isotope shifts in the energy levels of the singly ionized neodymium atom

Isotope shifts ΔT (142–144) have been evaluated for odd and even energy levels of the singly ionised neodymium atom from the measurements carried out in 168 spectral lines in the 3930–5820 Å region, employing a recording Fabry-Perot spectrometer and highly enriched isotopes excited in liquid-air cooled hollow cathodes. The electronic configurations 4f³5d6s, 4f³5d6p and 4f⁴6p could be assigned to some of the energy levels on the basis of the present study.     

A new method of calculating the piezo-electric constants of α-quartz

A method of calculating the piezo-electric constants of α-quartz is described which consists in determining the electric moment developed by changes of bond-lengths and bond-angles on strain. Considering three atoms P, Q, R, of which P and R are silicon atoms and Q an oxygen atom orvice-versa, the electric moment developed on strain may be resolved into moments in the plane PQR and moments perpendicular to this plane. Resolving these moments along the axes of the crystal and summing up for all the forty-two planes in the unit cell, we get the piezoelectric equations and constants of the crystal. The electric moment in the plane is equivalent to the moment produced by the change of bondlength along the direction of the bonds before strain, while for the moment normal to the plane we take the average value,i.e., half the value of the moment normal to the plane when the displacements of the atoms are wholly normal to the plane. The method gives good agreement with the observed values.