TY - JOUR
T1 - First-principles study of phase stability of bcc XZn (X=Cu, Ag, and Au) alloys
AU - Alsalmi, O.
AU - Sanati, M.
AU - Albers, R. C.
AU - Lookman, T.
AU - Saxena, A.
N1 - Funding Information:
This work was carried out under the auspices of the National Nuclear Security Administration of the US Department of Energy at Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396. We also acknowledge the generous amounts of computer time provided by Texas Tech University High Performance Computer Center. O.A. gratefully acknowledge the financial support from the Umm al-Qura University.
Publisher Copyright:
© 2018 American Physical Society. US.
PY - 2018/11/5
Y1 - 2018/11/5
N2 - First-principles density-functional theory is used to study the phase stability/instability and anomalies in the formation of the higherature bcc phases of XZn (X = Cu, Ag, and Au) alloys. Although from perhaps a naive point of view, their properties are expected to monotonically depend on the noble-metal (X) column position in the periodic table, this is not the case. For example, the middle-column AgZn alloy has a lower bcc order-disorder (critical) temperature than the CuZn and AuZn alloys above and below in the column. It is shown that this and other nonmonotonic behaviors can be explained in terms of a competition between atomic-size effects and X-atom d-orbital spatial extent. For example, charge-density studies and pair-potential modeling of XZn alloys show that the effective Ag-Zn bond is significantly weaker than either the Cu-Zn or Au-Zn bond at their respective equilibrium lattice constants. We find that an increased atomic-core size effect initially weakens the X-Zn bonding as one goes from CuZn to AgZn, but then the larger d-orbital spatial extent for higher principal quantum numbers becomes a more dominant effect and increases the bonding from AgZn to AuZn. This study is focused on the highly symmetric cubic higherature phases, where relative bond-strength magnitudes should be far more important than any bond-directionality effects; the lattice parameters, bulk moduli, elastic constants, Debye temperatures, heats of formation, and order-disorder temperatures for the bcc phases of the three XZn alloys are calculated and compared with experiment.
AB - First-principles density-functional theory is used to study the phase stability/instability and anomalies in the formation of the higherature bcc phases of XZn (X = Cu, Ag, and Au) alloys. Although from perhaps a naive point of view, their properties are expected to monotonically depend on the noble-metal (X) column position in the periodic table, this is not the case. For example, the middle-column AgZn alloy has a lower bcc order-disorder (critical) temperature than the CuZn and AuZn alloys above and below in the column. It is shown that this and other nonmonotonic behaviors can be explained in terms of a competition between atomic-size effects and X-atom d-orbital spatial extent. For example, charge-density studies and pair-potential modeling of XZn alloys show that the effective Ag-Zn bond is significantly weaker than either the Cu-Zn or Au-Zn bond at their respective equilibrium lattice constants. We find that an increased atomic-core size effect initially weakens the X-Zn bonding as one goes from CuZn to AgZn, but then the larger d-orbital spatial extent for higher principal quantum numbers becomes a more dominant effect and increases the bonding from AgZn to AuZn. This study is focused on the highly symmetric cubic higherature phases, where relative bond-strength magnitudes should be far more important than any bond-directionality effects; the lattice parameters, bulk moduli, elastic constants, Debye temperatures, heats of formation, and order-disorder temperatures for the bcc phases of the three XZn alloys are calculated and compared with experiment.
UR - http://www.scopus.com/inward/record.url?scp=85060598594&partnerID=8YFLogxK
U2 - 10.1103/PhysRevMaterials.2.113601
DO - 10.1103/PhysRevMaterials.2.113601
M3 - Article
AN - SCOPUS:85060598594
VL - 2
JO - Physical Review Materials
JF - Physical Review Materials
SN - 2475-9953
IS - 11
M1 - 113601
ER -