Sound Velocities in Concentrated Metal–Ammonia Solutions

Abstract

The velocity of 10 MHz sound waves in solutions of lithium, calcium and barium in ammonia are presented. The sound velocity in the lithium and calcium solutions exhibits a minimum which had not previously been detected. This minimum is a function of the metal concentration and of the temperature. Previous investigations of the sound velocity in potassium and sodium ammonia solutions did not reveal the presence of such a minimum. It is postulated that the minimum is an indication of compound formation in the solutions. Calculations of the sound velocity for the lithium–ammonia solutions are presented using the scheme of Schroeder and Thompson. Data on the saturation curve of the lithium–ammonia solutions is also presented.

Excitations of lithium ammonia complexes studied by inelastic x-ray scattering

“…Measurements of the velocity of ultrasound in the liquid show a narrow minimum in the sound velocity as a function of concentrations, which is also consistent with the formation of Li͑NH 3 ͒ 4 + complexes. 3 In the solid phase, both x-ray 4 and neutron-scattering 5 measurements indicate the formation of the complex ͑the neutron measurements use samples with deuterated ammonia͒. Peaks from pure Li and NH 3 are not seen, but the data are consistent with the formation of Li͑NH 3 ͒ 4 .…”

Velocity of Sound in Lithium–ND3 Solutions

“…1 along with the adiabatic compressibility for pure liquid NHa.7 Also shown are the respective sound velocities. The behavior exhibited by the sound velocity in the Li-NDa solutions 8 is quite similar to that seen in the Li-NHa solutions; the velocity does not change with concentration upon dilution until the saturation is passed, thus saturation in the Li-NDa solutions occurs at about 20.50 MPM as in the Li-NHa solutions. This implies that the intermolecular potential between the molecules 4099 does not change much upon the substitution of D2 for H2 in the liquid state.…”

Intermediate Range Order in Metal–Ammonia Solutions: Pure and Na-Doped Ca-NH3

“…While in the 4 MPM solutions, there is no angular correlation in the distribution of Ca ions, in the 10 MPM solution, we do find a slight dominance for a facial approach of one Ca(NH 3 ) 6 unit to the next, consistent with the bcc arrangement of the solid calcium hexammine structure, Ca(NH 3 ) 6 , formed at the pseudo-eutectic point whereby cooling any metallic Ca–NH 3 solution to 185 K excess NH 3 crystallizes out leaving only the expanded metal. 20 , 21 This expanded-metal hexammine crystallizes in the Im 3 m space group with a lattice constant, a o = 9.12 Å, and an octahedral orientation of NH 3 molecules around each Ca atom. 11 , 20 Bond distances in the crystal have been determined as r (Ca–N) = 2.56 Å and r (Ca–D) = 3.12 Å, correlations which we have now shown to persist into the liquid state, even upon further dilution by additional NH 3 as in the 4 MPM solution.…”