Solute Size and Valence Effect in Some Superconducting Alloys of Transition Elements

Abstract

The use of the concept of an effective electron-atom ratio, iV^ff, which contains a solute size correction (rather than the usual ratio N used in Matthias' rule), introduced earlier in correlating superconducting critical temperatures of some dilute solutions of transition elements of the 4th, 5th, and 6th columns in niobium, has been extended to include some other transition-metal solutes of columns 7, 8, 9, and 10 in niobium. The concept has also been tried on some other transition-metal solid solutions of wider range of composition. For these latter alloys the analysis reveals that peaks in the curve of T e versus electron-atom ratio occur at iV e ff~4.4 and ~6.6, whereas with the uncorrected electron-atom ratio, these peaks tend to occur near iV~4.7 and ~6.4. The variation of E e i with iV e ff for alloys of transition metals of columns 4 and 5 suggests that the maximum values of H C 2 also occur near iV e ff »4.4. Both peaks in T e versus N e tt and H C 2 versus iV e ff seem to be independent of whether the solvent or solute atom is in the 3d, 4d, or Sd series.

Superconducting alloys of interstitial compounds

“…Many attempts [8,[18][19][20][21][22][23][24][25][26][27][28] have been made to establish useful empirical formulae containing mass, volume and electronic factors, to correlate the rapidly growing list of superconducting compounds and alloys. Undoubtedly the best known o f these is the equation proposed by Matthias [24],…”

“…Consequently, various attempts have been made to modify equation (1) to give a more satisfactory quantit ative agreement with alloy and compound data. For example, in considering solid solution transi tion metal alloys based upon a given solvent metal, DeSorbo [26] suggested that the factor N should be modified to allow for the change of the effective number of electrons due to expansion or contraction of the lattice by the solute atoms. Thus N is replaced by a modified factor (2) where Vs and V^ are the unit cell volumes of the solvent metal and the i-th component metal respectively.…”

Superconducting Transitions of Amorphous Bismuth Alloys

“…12 Effects which might arise from the change in molar volume are expected to be negligible in the alloys considered, although they may be important for other alloys. [13][14][15][16] Brillouin-zone effects have also been seen at times, 8,17 although they are usually small. A sizeable shift in T c can result from precipitation.…”