Multiple effects of a martensitic transition in alpha-phase uranium: Valence fluctuations, CDWS, discommensurations and solitons?

Abstract

1. 1. The D 2h Pmnm space group recently reported for α'-phase U suggests the phase is that of a 2H close-packed layered structure (commensurate) resulting from a martensitic transformation. A 9R type of layering may also be possible under some circumstances. 2. 2. A model of Nagasawa (4), which explains the role of lattice softening in the matrix phase of the SME alloy agCd to give a distorted D 2h 13 Pmnm structure, is used to explain the probable mechanics of a martensitic α to α' phase transition in uranium. The importance of the orthorhombic structure is stressed. 3. 3. It is suggested that the Nagasawa model (4) is also relevant in explaining the appearance of valence fluctuation, CDWs, discommensuration, incommensurate and commensurate structures, SMEs and even solitons in the course of the martensitic α- U → α'- U transition 4. 4. The variability in the low-temperature physical property behavior of α-phase U is stressed. Sme experiments indicate that the room temperature orthorhombic structure is unchanged on cooling towards zero K. The above discussion may thus only be for the special case of a martensitic transformation. It is speculated that the tie-in between a martensitic transformation and valence fluctuations may be quite general. Valence instabilities may appear in other actinide systems showing lattice softening near a phase transformation, as well as in rare-earth meetallic alloys.