Design of atomistic models of the little-known palladium oxide PdO 2 - - PowerPoint PPT Presentation

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Design of atomistic models of the little-known palladium oxide PdO 2 - - PowerPoint PPT Presentation

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Design of atomistic models of the little-known palladium oxide PdO 2 Diana Fabuov 1 , K. Tokr 1,2 , M. Derzsi 1,3 1 Advanced Technologies Research Institute, Faculty of Materials Science and Technology in Trnava, Slovak University of

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SLIDE 1

Design of atomistic models of the little-known palladium

  • xide PdO2

Diana Fabušová1, K. Tokár1,2, M. Derzsi1,3

1Advanced Technologies Research Institute, Faculty of Materials Science and Technology in Trnava,

Slovak University of Technology in Bratislava, 917 24 Trnava, Slovakia

2Institute of Physics, Slovak Academy of Sciences, 845 11 Bratislava, Slovakia 3Center of New Technologies, University of Warsaw, Żwirki i Wigury 93, 02089 Warsaw, Poland

diana.fabusova@gmail.com

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SLIDE 2

INTRODUCTION

  • Palladium and its oxides are important catalyst in many catalytic reactions with

diversity of technological applications.

  • The only well studied and technologically exploited phase of palladium with
  • xygen is palladium monoxide PdO.
  • One polymorph of palladium dioxide PdO2 was also reported. It was obtained in

high-p,T synthesis [Shaplygin, 1978], but it is poorly characterized.

  • Existence of only one PdO2 polymorph is surprising since at least 5 polymorphs

are known for Pt dioxide PtO2.

  • Our aim is to predict other stable PdO2 polymorphs using Density Functional

Theory modelling.

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 2 Diana Fabušová: PdO2 from ab initio

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SLIDE 3

PdO2 modelled in known MO2 structures

  • 19 unique structural types were taken from ICSD

crystallographic database

  • DFT optimization was performed for the models after

substitution of the metal atom (M) for Pd: M→ Pd

  • Enthalpies of formation were calculated:
  • in respect to elements:

Pd+O2 -> PdO2 (ΔH1)

  • in respect to PdO:

PdO + ½O2 -> PdO2 (ΔH2)

  • Relative stability at high pressures.
  • Dynamical Stability calculations.

#

Modelled types

1 VO2 2 CaCl2 3 CoO2 4 Cdl2 5 BaSi2 6 Ni0,5Mn1.5O4 7 MnO2 8 α-PbO2 9 NbO2 10 Rutil 11 VO2 (oF96) 12 PdF2 13 Brookite 14 Anatase 15 VO2 (aP12) 16 VO2 (HT) 17 Fluorit 18 Pyrit 19 HgO2 The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 3 Diana Fabušová: PdO2 from ab initio

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SLIDE 4

PdO2 modelled in known MO2 structures

  • Basic building block in

all modelled strucures is

  • ctahedron [MO6]

#

Modelled types

1 VO2 2 CaCl2 3 CoO2 4 Cdl2 5 BaSi2 6 Ni0,5Mn1.5O4 7 MnO2 8 α-PbO2 9 NbO2 10 Rutil 11 VO2 (oF96) 12 PdF2 13 Brookite 14 Anatase 15 VO2 (aP12) 16 VO2 (HT) 17 Fluorit 18 Pyrit 19 HgO2

Porous structures Layered structures Rutile group Post-rutiles Fluorite group Complex structures

Structural families

M O

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 4 Diana Fabušová: PdO2 from ab initio

The modelled structures belong to 6 structural families.

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SLIDE 5

CRYSTAL STRUCTURES

Rutile group

Zig-zag chains

Types: brookite Types: rutile, CaCl2, α-PbO2, NbO2,

linear chains

  • Formed by infinite chains of edge-shared octahedra.
  • The chains are interconnected through corners.

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 5 Diana Fabušová: PdO2 from ab initio

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SLIDE 6

CRYSTAL STRUCTURES

Post-rutile group

Types: anatase Types: VO2 (HT)

  • In the post-rutile structures, the rutile-like chains of octahedra share apart from corners, also edges.
  • They are known also as compressed rutiles.

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 6 Diana Fabušová: PdO2 from ab initio

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SLIDE 7

CRYSTAL STRUCTURES

Layered structures

Types: CoO2, CdI2, BaSi2

Peroxo-bridge

Type: HgO2

  • Formed by layers of octahedra sharing edges.
  • Various stackings of layers are possible (AAA or ABAB stacking).
  • The layers can be interconnected by peroxo-bridges.

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 7 Diana Fabušová: PdO2 from ab initio

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SLIDE 8

CRYSTAL STRUCTURES

Porous structures

Type: VO2 Type: MnO2

  • Characteristic feaure of porous structures is presence of empty channels (1D voids).
  • The stuctures are formed by single or double rutile-like chains sharing corners.

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 8 Diana Fabušová: PdO2 from ab initio

Type: Ni0.5Mn1.5O

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SLIDE 9

COMPUTER DETAILS

  • All structure models were optimized with DFT functional PBE modified for

solids (PBEsol).

  • All models were optimized in the pressure range 0-100 kb.
  • DFT calculation were performed in program VASP.
  • Lattice dynamics was calculated in the program Phonopy.
  • Visualization of crystal structures was done in VESTA.

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 9 Diana Fabušová: PdO2 from ab initio

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SLIDE 10

PdO2: ENTHALPY OF FORMATION

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

  • 1,5
  • 1,2
  • 0,9
  • 0,6
  • 0,3

0,0

ΔH1: Pd+O2 → PdO2

ΔH1 [eV/FU]

  • All models stable in respect to Pd and O2
  • 13 models stable in respect to PdO and O2
  • All structures observed for PtO2 are stable

also for PdO2

  • Rutile structure (#10) is not the ground

state

  • Lowest-E structure is VO2 type

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 10 Diana Fabušová: PdO2 from ab initio

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SLIDE 11

PdO2: ENTHALPY OF FORMATION

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

  • 0,4
  • 0,1

0,2 0,5 0,8 1,1

  • 1,5
  • 1,2
  • 0,9
  • 0,6
  • 0,3

0,0

ΔH1: Pd+O2 → PdO2

ΔH2 [eV/FU] ΔH1 [eV/FU]

ΔH2: PdO+ ½O2 → PdO2

  • All models stable in respect to Pd and O2
  • 13 models stable in respect to PdO and O2
  • All structures observed for PtO2 are stable

also for PdO2

  • Rutile structure (#10) is not the ground

state

  • Lowest-E structure is VO2 type

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 11 Diana Fabušová: PdO2 from ab initio

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SLIDE 12

PdO2: ENTHALPY OF FORMATION

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

  • 0,4
  • 0,1

0,2 0,5 0,8 1,1

  • 1,5
  • 1,2
  • 0,9
  • 0,6
  • 0,3

0,0

ΔH1: Pd+O2 → PdO2

ΔH2 [eV/FU] ΔH1 [eV/FU]

ΔH2: PdO+ ½O2 → PdO2

  • All models stable in respect to Pd and O2
  • 13 models stable in respect to PdO and O2
  • All structures observed for PtO2 are stable

also for PdO2

  • Rutile structure (#10) is not the ground

state

  • Lowest-E structure is VO2 type

Palladium peroxides (O2

2-)

are unstable

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 12 Diana Fabušová: PdO2 from ab initio

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SLIDE 13

PdO2: ENTHALPY OF FORMATION

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

  • 0,4
  • 0,1

0,2 0,5 0,8 1,1

  • 1,5
  • 1,2
  • 0,9
  • 0,6
  • 0,3

0,0

ΔH1: Pd+O2 → PdO2

ΔH2 [eV/FU] ΔH1 [eV/FU]

ΔH2: PdO+ ½O2 → PdO2

  • All models stable in respect to Pd and O2
  • 13 models stable in respect to PdO and O2
  • All structures observed for PtO2 are stable

also for PdO2

  • Rutile structure (#10) is not the ground

state

  • Lowest-E structure is VO2 type

Polymorphs observed in PtO2

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 13 Diana Fabušová: PdO2 from ab initio

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SLIDE 14

PdO2: ENTHALPY OF FORMATION

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

  • 0,4
  • 0,1

0,2 0,5 0,8 1,1

  • 1,5
  • 1,2
  • 0,9
  • 0,6
  • 0,3

0,0

ΔH1: Pd+O2 → PdO2

ΔH2 [eV/FU] ΔH1 [eV/FU]

ΔH2: PdO+ ½O2 → PdO2

  • All models stable in respect to Pd and O2
  • 13 models stable in respect to PdO and O2
  • All structures observed for PtO2 are stable

also for PdO2

  • Experimentally observed rutile structure

(#10) is not the ground state

  • Lowest-E structure is VO2 type

Rutile type

(observed in experiment)

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 14 Diana Fabušová: PdO2 from ab initio

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SLIDE 15

PdO2: ENTHALPY OF FORMATION

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

  • 0,4
  • 0,1

0,2 0,5 0,8 1,1

  • 1,5
  • 1,2
  • 0,9
  • 0,6
  • 0,3

0,0

ΔH1: Pd+O2 → PdO2

ΔH2 [eV/FU] ΔH1 [eV/FU]

ΔH2: PdO+ ½O2 → PdO2

  • All models stable in respect to Pd and O2
  • 13 models stable in respect to PdO and O2
  • All structures observed for PtO2 are stable

also for PdO2

  • Rutile structure (#10) is not the ground

state

  • Lowest-E structure is VO2 type

Rutile type VO2 type

(ground state)

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 15 Diana Fabušová: PdO2 from ab initio

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SLIDE 16

PdO2: DYNAMICAL STABILITY

  • We have calculated impact of atomic

vibrations on crystal stability by calculation

  • f phonon dispersion curves.
  • Positive (real) values of energies indicate

dynamical stability.

  • Negative (imaginary) values of energies

indicate dynamical instability.

  • All PdO2 models that are stable in respect

to PdO are also dynamically stable.

  • Only rutile structure is dynamically

unstable.

  • Possible reasons:
  • Failure of DFT method,
  • different structure observed in experiment.

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 16 Diana Fabušová: PdO2 from ab initio

Phonon dispersion curves of PdO2 in VO2 type (dynamically stable)

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SLIDE 17

PdO2: DYNAMICAL STABILITY

  • We have calculated impact of atomic

vibrations on crystal stability by calculation

  • f phonon dispersion curves.
  • Positive (real) values of energies indicate

dynamical stability.

  • Negative (imaginary) values of energies

indicate dynamical instability.

  • All PdO2 models that are stable in respect

to PdO are also dynamically stable.

  • Only rutile structure, which was reported

experimentaly is dynamically unstable.

  • Possible reasons:
  • Failure of DFT method,
  • different structure observed in experiment.

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 17 Diana Fabušová: PdO2 from ab initio

BaSi2 α-PbO2 MnO2 Ni0.5Mn1.5O4 CaCl2 rutile

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SLIDE 18

PdO2: LATTICE PARAMETERS

No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

TYPE VO2 CaCl2 CoO2 Cdl2 BaSi2 Ni0.5Mn1.5O4 MnO2 α-PbO2 NbO2 rutile rutile experiment SPGR Pnma Pnnm C2/m P63mc P-3m1 Fd-3m I4/m Pbcn I41/a P42/mnm a [Å] 4.573 4.503 5.283 3.051 3.05 8.559 10.017 4.487 17,998 4,500 4.495 4.483 b [Å] 9.311 4.447 3.05 3.051 3.05 8.559 10.017 5.448 17,998 4,500 4.495 4.483 c [Å] 3.054 3.095 5.74 8.913 4.419 8.559 3.075 5,072 2,536 6,228 3,114 3.158 3.101 β [°] 128.1 V [ų]/Z 32.5 31 36.4 35.9 35.6 39.2 38.6 31 31.5 31.9 31.6 Z 4 2 2 2 1 16 8 4 32 2 2

  • Calculated lattice parameters of the rutile

structure compare well with the measured values.

  • CaCl2 type has also lattice parameters

comparable to experimental values.

  • All other models have quite distinct lattice

parameters.

  • CaCl2 type is in fact orthorhombic rutile,

which differs only slightly from the ideal tetragonal rutile lattice.

  • So the question arises if the orthorhombic

rutile could be the experimentally observed structure instead of the tetragonal one.

Shaplygin et al., Zhurnal Neorganicheskoi Khimii, 23, 884 (1978).

Calculated lattice parameters for the lowest-energy polymorphs

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 18 Diana Fabušová: PdO2 from ab initio

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SLIDE 19

PdO2: LATTICE PARAMETERS

  • Here we show the calculated Infrared spectra for the

tetragonal and orthorhombic rutile (CaCl2) and VO2 type together with the experimental one.

  • Calculated frequencies and intensities for both rutile

and CaCl2 type structure correlate well with the experiment.

  • Calculated IR spectrum for the ground states VO2

type structure does not correlate with the measured spectrum.

B3u B2u B2u B3u B1u B3u B2u 190 290 390 490 590 690 790 intensity

CaCl2

190 390 590 790 Transmitance (a.u.)

IR spectra

Eu A2u Eu 190 290 390 490 590 690 790 intensity

rutile

Goncharenko, et al., Zhurnal Neorganicheskoi Khimii,1985.

measured

B3u B1uB1u B3u B2u B3u B1u B2u B1u B3u

190 390 590 790 intensity frequency [cm-1]

VO2

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 19 Diana Fabušová: PdO2 from ab initio

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SLIDE 20

PdO2: HIGH PRESSURES

  • Since the only known polymorph was obtained at

high pressures, we have optimized the 10 lowest- E models under various hydrostatic pressures up to 100 kb.

  • The plot shows relative energies of the models in

function of pressure.

  • Orthorhombic rutile (CaCl2) becomes the ground

state above 20 kb.

  • The high-pressure calculations predict formation
  • f orthorhombic rutile structural type under

pressure.

  • On the other hand, tetragonal rutile becomes

even more unstable under pressure and remains also dynamically unstable. Relative energies vs. pressure

The 2nd International Online Conference on Crystals 10-20 NOVEMBER 2020 ONLINE 20 0,05 0,1 0,15 0,2 0,25 0,3 0,35 0,4 0,45 0,5 20 40 60 80 100 ∆E = E-E0 [meV/FU] p [kb]

Ni0,5Mn1,5O4 MnO2 rutile CoO2 Cdl2 NbO2 BaSi2 PbO2_alpha VO2 CaCl2

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SLIDE 21

PdO2: SUMMARY

  • We have modelled PdO2 in 19 structural types observed for MO2 oxides.
  • All models are stable relative to Pd + O2.
  • 13 structures are stable in respect to well-known PdO.
  • Tetragonal rutile (claimed in experiment) is only 10th lowest in energy.
  • All models accept tetragonal rutile are dynamically stable.
  • The ground state structure at low pressure is VO2 type structure and at high pressures
  • rthorhombic rutile.
  • Measured PdO2 structure and IR spectrum could be interpreted based on
  • rthorhombic variant of rutile.
  • Overall we predict rich polymorphism for PdO2 compound comparable to PtO2.

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SLIDE 22

ACKNOWLEDGEMENTS

  • The European Regional Development Fund, Research and Innovation

Operational Programme, for project No. ITMS2014+: 313011W085;

  • Scientific Grant Agency of the Slovak Republic, grant No. VG 1/0223/19;
  • The Slovak Research and Development Agency, grant No. APVV-18-0168;
  • Aurel supercomputing infrastructure in CC of Slovak Academy of

Sciences acquired in projects ITMS 26230120002 and 26210120002 funded by ERDF

Thank you for your attention ☺

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