Phase transformations in cerium and thorium metals at ultra high pressures

Journal Article · Sun Dec 01 00:00:00 EST 1991 · Scripta Metallurgica; (United States)

DOI:https://doi.org/10.1016/0956-716X(91)90157-V· OSTI ID:5340593

Vohra, Y K ^[1]

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1. Materials Science and Engineering, Cornell Univ., Ithaca, NY (US)

This paper reports on the role of pressure variable in phase transformation which has not been fully exploited in metallic elements and their alloys. The static compression of over 50% in volume can readily be obtained in most metals and this tremendous change in inter-atomic distances can lead to the formation of new exotic crystal structures. The pressure-induced electron transfer amongst existing electronic energy bands and the occupation of new bands are the driving forces in a rich variety of phase transformations. The modern high pressure diamond anvil cell techniques can produce calibrated static pressures of over 300 to 400 GPa range and this technology, when interfaced with the synchrotron radiation sources, can yield rapid structural information (1-3). These capabilities have given new impetus for investigation of phase transformations in metallic systems at extreme conditions of temperatures and pressures and in establishing phase boundaries at high pressures and high temperatures. Cerium (Ce) and thorium (Th) metals occupy special positions in the periodic table at the beginning of the 4-f lanthanide and 5-f, actinide series, respectively. Ce has one electron in the localized 4-f shell, apart from the three valence electrons. Th metal, on the other hand, has four valence electrons and an unoccupied 5-f band above the Fermi-energy at ambient conditions. In view of the unoccupied 5-f band, Th metal is normally regarded as a tetravalent transition metal like Ti, Zr, and Hf and its bonding and other electronic properties can be explained within the tetravalent transition metal framework. However, the application of ultra-high pressures causes the delocalization of the 4-f shell in Ce and it is believed that Ce above 0.8 GPa pressure is a 4-f band metal.

• OSTI ID: 5340593
• Journal Information: Scripta Metallurgica; (United States), Vol. 25:12; ISSN 0036-9748
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
74 ATOMIC AND MOLECULAR PHYSICS
CERIUM
PHASE TRANSFORMATIONS
THORIUM
COMPRESSION STRENGTH
CRYSTAL STRUCTURE
FERMI INTERACTIONS
FERMI LEVEL
HIGH PRESSURE
TEMPERATURE RANGE 0400-1000 K
TRANSITION ELEMENTS
ACTINIDES
BASIC INTERACTIONS
ELEMENTS
ENERGY LEVELS
INTERACTIONS
MECHANICAL PROPERTIES
METALS
RARE EARTHS
TEMPERATURE RANGE
WEAK INTERACTIONS
360102* - Metals & Alloys- Structure & Phase Studies
360103 - Metals & Alloys- Mechanical Properties
664100 - Theory of Electronic Structure of Atoms & Molecules- (1992-)