Laser calorimetric or thermal rise techniques are useful for the determination of very low absorption coefficients in solids. A number of improvements in this technique are described of which the most important is a means of separating surface and bulk absorption. These techniques have been applied to study alkali halides in the ir but are applicable where laser sources of sufficient power are available.

The Hall coefficient ($R$) for homogeneous potassium single crystals was measured at 4.2\ifmmode^\circ\else\textdegree\fi{}K in magnetic fields ($H$) up to 85 kG. Above 15 kG, $R$ approached $H$-independent values in excellent agreement with free-electron calculations. Thus, the Fermi surface must be simply connected. Below 15 kG, $R$ exhibited weak $H$ dependence stemming almost unambiguously from scattering anisotropy (due predominantly to phonons). At low $H$, $R$ is compared with pseudopotential calculations. Correlations between $R$ and magnetoresistance are identified for either scattering or inhomogeneity phenomena.

Shubnikov-de Haas oscillations have been observed in n-type Cd3P2. From an analysis of the temperature dependence of the amplitude of the oscillations the conduction band effective mass was found to be 0.06 mo for n = 1.2 × 1018 cm-3 and 0.05 mo for n = 2.2 × 1017 cm-3.

A new model is proposed in which the observed magnetoresistance curves for potassium are qualitatively analyzed as a synthesis of four superposed behaviors: (1) a phonon saturating behavior exhibiting the predicted temperature dependence for umklapp scattering, (2) a new residual saturating behavior due to impurities and defects, (3) a negative saturating behavior agreeing quantitatively with size-effect theory, and (4) a newly identified low-field quadratic behavior which becomes asymptotically linear at high fields due to macroscopic inhomogeneities.

Gehalte an Germanium bzw. Kupfer im β-Titan-Niob-Mischkristall von Legierungen mit etwa 50 Gew.% Nb (Drähte 1,0 mm Ø) vermindern das kritische Magnetfeld Hc der binären Legierung um etwa 10 kG/% Ge bzw. 4 kG/% Cu. Aufgrund von Hc-Messungen kann angenommen werden, dass bei 700 °C unter 0,5% Ge bzw. über 1% Cu in der Matrix gelöst sind. Bei einem Gehalt von 2% Ge in 97% kalt-verformten Proben mit etwa 50% Nb erreicht Hc nach 250 h bei 400 °C 117,7 kG, bei einem Gehalt von 4% Ge nach 16 h bei 500 °C 119,4 kG. Der höchste Hc-Wert der nach 400 °C-Auslagerung untersuchten binären Legierungen (TiNb55 mit 117,5 kG) wird in diesen Fällen durch günstige Niobanreicherung in der Matrix überschritten. Die Löslichkeit von Germanium im β-Mischkristall ist bei 400 ° C sehr gering und Ti5Ge3 wird gebildet. Die kupferhaltigen Legierungen erreichen trotz dieser Niobanreicherung in der Matrix nicht die Hc-Werte der germaniumhaltigen Legierungen, da die Löslichkeit des Kupfers im β-Mischkristall höher ist als die des Germaniums. Zusätze von 2 At.% Sn, Ga, In, Fe, Mn, Cr, Al, Zr, Ag oder Ge vermindern in der genannten Reihenfolge abnehmend Hc von 97% kaltverformten und 10 h bei 400 ° C ausgelagerten 1 mm Ø Drähten der Legierung mit 50 Gew.% Nb, während durch einen Zusatz von 2 At.% Cu Hc gegenüber TiNb50 mit 114 kG nicht verändert wird und durch den Zusatz von 2 At. % Ni auf 116,1 kG ansteigt.

The theoretically predicted and long-sought intrinsic saturation of the transverse magnetoresistance of the alkali metals has finally been observed after sufficiently reducing the masking effect of the large superimposed linear magnetoresistance which is attributed to such classical considerations as geometry, Hall angle and non-uniform current distribution. The observed saturation values were about 100 times smaller than those observed previously in complicated metals but were still much too large to be explained only by Fermi surface anisotropy. The saturation phenomena contradict Kohler's rule but can be plausibly explained by mean free path anisotropy due predominantly to electron-phonon scattering mechanisms.

Received 25 September 1967DOI:https://doi.org/10.1103/PhysRevLett.19.1428©1967 American Physical Society

Conduction band structure in n-type strontium titanate investigated by measuring oscillatory magnetoresistance in high magnetic fields

The magnetoresistance of semiconducting SrTi${\mathrm{O}}_{3}$ has been investigated in high magnetic fields (up to 150 kOe). In the temperature range 1.4-2.1 \ifmmode^\circ\else\textdegree\fi{}K, for fields of more than 50 kOe, well-developed Shubnikov-de Haas-type oscillations have been observed. The data support a conduction band consisting of spheroids along the $〈100〉$ crystalline axes, having 3 minima at the points ${X}_{3}$. The periods of oscillation as well as the temperature dependence of the amplitude and the magnetic fields saturation lead to the following values for the transverse and longitudinal effective masses: ${m}_{t}=1.5{m}_{0}\ifmmode\pm\else\textpm\fi{}15%$; ${m}_{l}=6.0{m}_{0}\ifmmode\pm\else\textpm\fi{}30%$.

Received 2 February 1965DOI:https://doi.org/10.1103/PhysRevLett.14.360©1965 American Physical Society