A Phase Transition and the Photoemissive Quantum Yield at Low Temperatures in Cs₃Sb Films

Abstract

By means of a recently developed method the photoemissive quantum yield (Y) of Cs,Sb films is measured as a function of temperature at very low light intensities. A strong evidence for the existence of Cs,Sb in two phases one of which (phase 11) is the known "state" with high Y is found. The other phase (I) has a much lower Y which depends strongly on the light intensity. Phase I exists only below (260 f 2) OK: above this temperature it transforms to phase 11. The existence of phase I up to now was not noticed because i t is very sensitive to the absorbed light energy which easily can convert it to phase 11. We suggest for phase I the regular body-centred cubic structure and for phase I1 the pseudo-body-centred cubic structure found a t room temperature by Jack and Wachtel. Moreover, we propose for Cs,Sb an energy band structure with a split valence band. The observed dependences of Y on temperature and light intensity are discussed in this framework. Even other Cs,Sb properties seem to fit rather well the proposed energy band and crystal structure.Die Quantenausbeute ( Y) des iiuBeren lichtelektrischen Effektes von Cs,Sb-Dunnschichten wird mittels einer neuen Methode als Funktion der Temperatur bei sehr niedrigen Lichtintensitaten gemessen. Es ergab sich ein deutlicher Hinweis, daB Cs,Sb in zwei Phasen existiert, von denen eine (Phase 11) dem bekannten Zustand mit hohem Y entspricht. Die andere Phase (I) hat einen vie1 niedrigeren Wert von Y, der stark von der Lichtintensitit abhiingig ist. Die Phase I existiert nur unterhalb (260 2) OK. Oberhalb dieser Temperatur verwandelt sie sich in die Phase 11. Die Existenz der Phase I war bisher nicht bekannt, weil sie fur die absorbierte Lichtenergie sehr empfindlich ist, welche sie sehr leicht in die Phase I1 verwandeln kann. Wir schlagen fur die Phase I die reguliir kubisch-raumzentrierte Gitterstruktur vor und fur die Phase I1 die pseudo kubisch-raumzentrierte Gitterstruktur ; letztere wurde von Jack und Wachtel bei Zimmertemperatur gefunden. Ferner schlagen wir fur Cs,Sb eine Energiebandstruktur mit aufgespaltenem Valenzband vor. Die beobachtete Abhiingigkeit von Y von der Temperatur und der Lichtintensitit wird in diesem Rahmen diskutiert. Es scheint, daB auch die anderen Eigenschaften von Cs,Sb mit der vorgeschlagenen Energieband-und Kristallstruktur im wesentlichen ubereinstimmen.

Electronic structure of alkali-pnictide compounds

“…The comparison of the Ai2 data for the octet compounds compiled in table 4 would suggest that the bonding is slightly more covalent in the AsNa, structure.…”

“…Thus the electronic DOS of the alkali-bismuth Laves phases is very similar to that of the alkali-lead Laves phases and is related to the electronic structure of the alkali-lead (tin) cluster compounds. In the equiatomic alkali-lead (tin) compounds, tetrahedral Pb:-clusters are stabilized by covalent threecentre bonds as in P, molecules [4]. This bond is very strong and is also found in the molten alloys and in the KPb, Laves phase.…”

Ab initio study of the crystal and electronic structure of mono- and bi-alkali antimonides: Stability, Goldschmidt-like tolerance factors, and optical properties

“…1a) as the crystal structure for mono-and bi-alkali antimonides, X 2 YSb (X and Y are Group I alkali metals). 1,[7][8][9][10][11][12][13][14][15][16][17] However, a very recent publication on the first ever successful epitaxial growth of Cs 3 Sb finds that, although the thin-film structure is cubic and single crystal, it is not clear whether the structure is D0 3 or some other cubic phase with lower symmetry. 5 To complicate the matter, the Materials Project database 18 reports imaginary phonon frequencies and thus mechanical instability for Cs 3 Sb in the D0 3 structure.…”

A 133Cs-NMR Study of the Chemical Bonding of the Solid Compound Semiconductor Cs3Sb

“…[2] indicating only slight energy differences between these structures. In the case of Cs3Sb only the cubic structure has been reported so far [3], where below 260 K De Munari et al [4] suggest that there is an ordered arrangement of the Cs atoms with Oh 5 symmetry, although at room temperature it has been assumed by Jack and Wachtel [3] that the Cs-Sb sublattice is partially disordered.…”