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Li, Mingkai
Publications (3 of 3) Show all publications
Long, D., Li, M., Meng, D., He, Y., Yoon, I. T., Ahuja, R. & Luo, W. (2018). Accounting for the thermo-stability of PdHx (x=1-3) by density functional theory. International journal of hydrogen energy, 43(39), 18372-18381
Open this publication in new window or tab >>Accounting for the thermo-stability of PdHx (x=1-3) by density functional theory
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2018 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 43, no 39, p. 18372-18381Article in journal (Refereed) Published
Abstract [en]

We calculate the formation enthalpies of PdHx (x = 0-3) by cluster expansion (CE) and calculations based on density functional theory. CE predicts the stable palladium hydride structures PdH, PdH2.62, and PdH2.75. The band structures and density of states indicate that the amount of hydrogen in the palladium lattice does not alter the metallic character of the palladium significantly. However, all PdH X structures with x > 1 have greater formation enthalpies than that of the given reaction path 4PdH(2) = 2PdH + 2Pd + 3H(2) and thus they are thermodynamically unstable. The shorter bond length of Pd-H and the smaller bond angle of Pd-H-Pd imply a higher cohesive energy in zincblende (ZB) PdH than that in rocksalt (RS) PdH. Bader charge analysis shows a stronger electronegativity of H atoms in ZB-PdH than that in RS-PdH. This results in a stronger Pd-H bond in ZB-PdH than that in RS-PdH. Thus ZB-PdH has lower formation enthalpy than that of RS-PdH. However, regarding the dynamic stability, we conclude that hydrogen atoms prefer to occupy the octahedral sites of the palladium lattice because of the lower zero-point energy and vibration free energy than that of occupying the tetrahedral sites. 

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2018
Keywords
PdHx, Cluster expansion method, Density functional theory, Formation enthalpy, Thermodynamic stability, Dynamic stability
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-368759 (URN)10.1016/j.ijhydene.2018.08.030 (DOI)000446949400032 ()
Available from: 2018-12-07 Created: 2018-12-07 Last updated: 2018-12-07Bibliographically approved
Li, M., Long, D., Ahuja, R. & He, Y. (2017). Magnetic order and phase diagram of magnetic alloy system: MgxNi1-xO alloy. Physica status solidi. B, Basic research, 254(9), Article ID 1700085.
Open this publication in new window or tab >>Magnetic order and phase diagram of magnetic alloy system: MgxNi1-xO alloy
2017 (English)In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 254, no 9, article id 1700085Article in journal (Refereed) Published
Abstract [en]

The antiferromagnetic phase diagram of MgxNi1-xO alloy was reexamined theoretically by multicomponent cluster expansion method. It predicts antiferromagnetic state in the alloy with high Mg content, instead of a mixture of antiferromagnetic and paramagnetic states, which was deduced previously from neutron diffraction results. The theoretically found intermediate antiferromagnetic ground states at Mg contents of x(Mg) = 0.25 and 0.75 exhibit very low neutron diffraction intensities, which leads to confusion with paramagnetic state. Our approach here reduced remarkably the computation time in searching the intermediate ground states as well as calculating the magnetic phase diagram.

Keywords
density functional theory, magnetic alloys, magnetic order, MgxNi1-xO, phase diagram
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-335869 (URN)10.1002/pssb.201700085 (DOI)000410648500020 ()
Funder
Swedish Energy AgencySwedish Research CouncilStandUp
Available from: 2018-01-22 Created: 2018-01-22 Last updated: 2018-01-22Bibliographically approved
Long, D., Li, M., Luo, M., Zhu, J., Yang, H., Huang, Z., . . . He, Y. (2017). Theoretical investigation on thermodynamic properties of ZnO1-Te-x(x) alloys. MATERIALS RESEARCH EXPRESS, 4(5), Article ID 055901.
Open this publication in new window or tab >>Theoretical investigation on thermodynamic properties of ZnO1-Te-x(x) alloys
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2017 (English)In: MATERIALS RESEARCH EXPRESS, ISSN 2053-1591, Vol. 4, no 5, article id 055901Article in journal (Refereed) Published
Abstract [en]

In this study, the formation energy, phase diagram (with/without phonon contribution) and the relationship between bond stiffness and bond length for wurtzite (WZ) and zincblende (ZB) structures of ZnO1 Te-x(x) (0 <= x <= 1) alloys have been investigated by combining first-principles calculations and cluster expansion method. The formation energy of ZnO1-Te-x(x) alloys is very high in both structures, which means that it is difficult for ZnO and ZnTe to form stable ternary alloys ZnO1-Te-x(x). In the phase diagrams, both structures do not have stable phase of ternary alloys and ZnO1-Te-x(x) ternary alloys can only exist in the form of metastable phase. These results indicate that ZnO and ZnTe easily form solid solubility gap when they form alloys. After considering vibrational free energy, we found the solubility of Te in ZnO and O in ZnTe was increased and the vibrational entropy improved the solubility furthermore. The phonon contribution is not ignorable to improve solid solubility. The phonon density of states was analyzed for ZnO1-Te-x(x) alloys and the contribution from vibrational entropy was discussed.

Keywords
solubility, ZnO1-Te-x(x) alloy, cluster expansion method, phase diagram, vibration free energy, vibration entropy
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-323444 (URN)10.1088/2053-1591/aa6d23 (DOI)000400914900001 ()
Available from: 2017-07-06 Created: 2017-07-06 Last updated: 2017-07-06Bibliographically approved
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