Pressure-induced changes in protactinium metal: Importance to actinide-metal bonding concepts

Protactinium occupies an important position in the actinide series of elements, as it represents the first of four elements (Pa-Pu) having $5f$-electron character in their bonding at atmospheric pressure. We have determined in experimental studies with synchrotron radiation to 130 GPa, that the tetragonal structure of protactinium (space group $I4/mmm)$ converts to an orthorhombic, alpha-uranium structure (space group Cmcm) at 77(5) GPa, where the atomic volume has been reduced by \ensuremath{\sim}30%. This structural change is interpreted as reflecting an increase in $5f$-electron contribution to the bonding in protactinium over that initially present, becoming more similar to that present in alpha-uranium metal at atmospheric pressure. We determined experimentally that this structural transformation occurred at significantly higher pressures and at a smaller atomic volume than predicted by theory. The experimental results reported here represent the highest pressures under which protactinium metal has been studied.

[1]  H. Blank.  Experimental results on properties of Pa revisited , 2002 .

[2]  J. R. Peterson,et al.  X-ray diffraction study of protactinium metal to 53 GPa , 1982 .

[3]  A. Pasturel,et al.  Equilibrium properties of δ-Pu : LDA + U calculations (LDA ≡ local density approximation) , 2000 .

[4]  F. Birch.  Finite Elastic Strain of Cubic Crystals , 1947 .

[5]  J. Spirlet,et al.  Superconducting Properties of Protactinium , 1979, Science.

[6]  Y. Wu,et al.  Static EOS of uranium to 100 GPa pressure , 1990 .

[7]  Y. Vohra,et al.  Phase transformations and equation of state of praseodymium metal to 103 GPa , 2000 .

[8]  P. Söderlind.  First-principles elastic and structural properties of uranium metal , 2002 .

[9]  Y. Vohra,et al.  {alpha}-uranium phase in compressed neodymium metal , 2000 .

[10]  O. Eriksson,et al.  Pressure-induced phase transitions in Pa metal from first-principles theory , 1997 .

[11]  G. Kotliar,et al.  Correlated electrons in δ-plutonium within a dynamical mean-field picture , 2001, Nature.

[12]  W. Zachariasen.  Crystal chemical studies of the 5f-series of elements. XVI. Identification and crystal structure of protactinium metal and of protactinium monoxide , 1952 .

[13]  R. Ahuja,et al.  Delocalization and new phase in americium: Density-functional electronic structure calculations , 2000 .

[14]  M. Bradbury.  The vapour pressure of protactinium metal , 1981 .

[15]  K. Litfin,et al.  Pressure induces major changes in the nature of Americium's 5f electrons. , 2000, Physical review letters.

[16]  K. Litfin,et al.  High-Pressure Studies of Americium Metal. Insights into its Position in the Actinide Series. , 2001 .

[17]  M. Pénicaud.  Calculated structural stabilities of U, Np, Pu and Am; new high-pressure phases for Am and Pu , 2002 .

[18]  W. Zachariasen,et al.  Crystal chemical studies of the 5f-series of elements. XXIV. The crystal structure and thermal expansion of γ-plutonium , 1955 .

[19]  B. Johansson,et al.  Electronic structure of the actinide metals , 1982 .

[20]  Per Söderlind,et al.  Ambient pressure phase diagram of plutonium: A unified theory for α-Pu and δ-Pu , 2001 .

[21]  Juan Rodríguez-Carvajal,et al.  Recent advances in magnetic structure determination by neutron powder diffraction , 1993 .

[22]  Y. Vohra,et al.  5f bonding in thorium metal at extreme compressions: Phase transitions to 300 GPa. , 1991, Physical review letters.

[23]  W. Zachariasen.  ON THE CRYSTAL STRUCTURE OF PROTACTINIUM METAL , 1959 .

[24]  W. Müller,et al.  Preparation and structure studies of “Van Arkel” protactinium , 1978 .

[25]  B. Johansson,et al.  Calculated bulk properties of the actinide metals , 1978 .

[26]  P. Söderlind.  Delocalization and phase transitions in Pr: Theory , 2002 .

[27]  Per Söderlind,et al.  Theory of the crystal structures of cerium and the light actinides , 1998 .

[28]  C. S. Barrett,et al.  Crystal Structure Variations in Alpha Uranium at Low Temperatures , 1963 .

[29]  Peter M. Bell,et al.  Calibration of the ruby pressure gauge to 800 kbar under quasi‐hydrostatic conditions , 1986 .

[30]  M. Pénicaud.  Calculated equilibrium properties, electronic structures and structural stabilities of Th, Pa, U, Np and Pu , 2000 .

[31]  M. McMahon,et al.  Different Results for the Equilibrium Phases of Cerium above 5 GPa , 1997 .