Formation of Palladium Hydrides Layers in Reactive Plasmas

Transcription

1 Formation of Palladium Hydrides Layers in Reactive Plasmas H. Wulff 1, M. Froehlich 2, 1 University of Greifswald, Institute of Physics, Greifswald, Felix-Hausdorff-Str. 6, Germany, 2 Leibniz Institute for Plasma Science and Technology e.v., Felix-Hausdorff-Str. 2, Greifswald, Germany Mühlleithen

2 Outline (i) Motivation and experimental setup (ii) Incorporation of hydrogen (iii) Influence of temperature exposure (iv) Influence of substrate voltage and time of plasma treatment (v) Conclusions

3 Outline (i) Motivation and experimental setup (ii) Incorporation of hydrogen (iii) Influence of temperature exposure (iv) Influence of substrate voltage and time of plasma treatment (v) Conclusions

4 Hydrogen Relevance Hydrogen has the highest gravimetric energy density Hydrogen Petroleum gas Methane Gasoline Diesel fuel Methanol 33,3 kwh/kg 10,6-13,1 kwh/kg 13,9 kwh/kg 12 kwh/kg 11,9 kwh/kg 5,47 kwh/kg Applications Fuel cell automotive, submarine, portable devices

5 Hydrogen storage Storage Compressed Liquid gas Metal hydride Adsorption (porous material) Graphite nano fibres

6 Storage as metal hydride Current status - Most binary metal hydrides synthesized by solid gas reaction between metal and hydrogen. - Some metals and intermetallic compounds easily take up hydrogen, - Other form hydrides only under high hydrogen pressure up to 10 9 Pa. up to now hydrogen rich metal hydride phases are described to form only at high pressure (> 2 kbar) 1,2 1 B. Baranowski et al., J. Alloys Comp. 404 (2005) 2 2 V.E. Antonov, J. Alloys Comp. 330 (2002) 110

7 Formation enthalpy and hydrogen storage properties H 2 gaseous: g/l H 2 liquid: 70.9 g/l PdH 0.7 : 72 g/l PdH 1.33 : 137g/l

8 Why using plasma? Plasma - Chemical reactivity in solids directly affected by plasma - Processes taking place under vacuum conditions Of high interest - Investigation and characterization of structural changes, new reaction pathways - Plasmachemical processes

9 Chemical reactions in plasma enhanced vapour deposition processes

10 Experimental Setup mass flow controller Process parameters Working pressure 4*10-1 mbar gas Ar/H 2 gas flow 20 sccm microwave power process time 700 W 10 min to 1 h microwave incoupling substrate holder thin Me- films Material Si / 800 nm SiO 2 /1 nm Cr / 20 nm Pd Dr. Ellmer, HC Berlin Methods Microwave Ar/H 2 -Plasma, P = 700W, variation of substrate bias and treatment time, no additional substrate heating Grazing Incidence X-ray Diffractometry (GIXD, Göbelmirror), in-situ HT GIXD, X-ray Reflectometry (XR),

11 Outline (i) Motivation and experimental setup (ii) Incorporation of hydrogen (iii) Influence of temperature exposure (iv) Influence of substrate voltage and time of plasma treatment (v) Conclusions

12 Hydrogen incorporation discontinuously intensity / cps GIXD 111 fcc Pd Ar/H 0 V bias 0 35 incorporation 40 of H Without plasma no incorporation of H in vacuum - With plasma Smaller angles higher lattice constants fcc Bias voltage 0 V 45 min 30 min 15 min as deposited Formation of PdH x 2 /

13 Hydrogen incorporation substrate bias -50 V intensiy /cps V, 15 min as-deposited PdH x / Bias voltage -50 V Fast formation of PdH x by using bias voltage

14 Lattice constants of PdH x after plasma exposure Ar/H 2 plasma, 700 W PdH x -50 V bias ß- PdH x ; x < lattice constant / A PdH x 0 V bias two different PdH x phases 3.90 Pd, as deposited time / min α- PdH x ; x < F.D. Manchester, A. San Martin, J.M. Pitre J. Phase Equilib.15 (1994) 62-83

15 fcc lattice with octahedral interstices Pd H Pd Assumption of H incorporation H

16 Volume changes in PdH x Fukai 1, Somenkov 2 et al.: High pressure experiments: Hydrogen in d-metals is almost incompressible! For fcc Ni, fcc Pd Δv H = 2.5 Å 3 (Volume change by adding H) if V V U U v H c H N V const Me U v the volume change in the unit cell depends linearly on the hydrogen concentration 1 Y. Fukai, The Metal hydrogen System, Springer V.A. Somenko et al. J.Less Common Met. 129, (1987) 171 H with V N c U Me H holds: V V N N U H Me U caused by N (the volume per metal atom) c H U H VU V v hydrogen atoms H

17 Volume changes in PdH x c H VU V v U H Determination of H concentration 4,10 PdH 0.14 fcc α-pdh x c H = 0.14 fcc ß-PdH x c H = 0.55 PdH ,05 reference values 3 fcc PdH x PdH 0.64 PdH 0.97 lattice parameter / A 4,00 3,95 3,90 Pd PdH 0.6 PdD 0.64 PdH Linear behaviour R = Vegards rule reference values c H = ,85 0,0 0,2 0,4 0,6 0,8 1,0 hygrogen content / mol PdH Y. Fukai, The Metal hydrogen System, Springer V.A. Somenko et al. J.Less Common Met. 129, (1987) ICSD, FIZ Karlsruhe, release 2014

18 Outline (i) Motivation and experimental setup (ii) Incorporation of hydrogen (iii) Influence of temperature exposure (iv) Influence of substrate voltage and time of plasma treatment (v) Conclusions

19 High temperature exposure HTGIXD High temperature GIXD intensity /cps after hydrogen desorption (400 C) the Pd crystallinity increases, and decreases again at 700 C 0 38,0 38,5 39,0 39,5 40,0 40,5 41,0 diffraction angle 2 / C C C C C C Bias voltage -50 V Hydrogen desorption for temperatures higher than 300 C

20 High temperature exposure in-situ HTGIXD Lattice constants vs. time 4,00 3,98 RT Temperature [ C] PdH PdH x -50 V substrate voltage HT diffractometry bias voltage -50 V lattice parameters / A 3,96 3,94 3,92 3,90 3,88 Ref: fcc Pd RT Remarkable decrease of lattice constants for T > 370 C 3, time / min

21 Outline (i) Motivation and experimental setup (ii) Incorporation of hydrogen (iii) Influence of temperature exposure (iv) Influence of substrate voltage and time of plasma treatment (v) Conclusions

22 Influence of bias voltage on lattice constants 15 min treatment time intensity / cps 800 as deposited -50 V -100 V V U bias > -50 V increased lattice constants U bias < -50 V decrased lattice constants [ ]

23 Temporal variation of the lattice parameters lattice parameters/ A 3,90 3,89 3,88 3,87 3,86 3,85 3, V fcc Pd 40 Pa, 250 C Y. Fukai et al., J. Alloy Comp., 313 (2000) 121 3,83 Ar/H 2 plasma substrate 3,82 bias -100 V working 3,81 pressure 40 Pa temperature C Assumption Formation of Vacancies Pd vac smaller lattice parameters time / s

24 Imperfections of the first type: point defects lattice deformation due to vacancies based on the elastic theory ICMCTF 2005, San Diego

25 Model Fukai : Pd 4 H 4 transformation into Pd 3 H 4 by high pressure treatment The crystal structure of fcc-based mono-hydride of NaCl-type (a), and vacancy-ordered M3VacH4 (b). In the vacancy-ordered structure, one of the four simple-cubic M-sublattices become vacant (L12 structure of Cu3Au type), with octahedral interstitial sites filled with H atoms. fcc Pd4 ρ = g/cm 3 fcc Pd 4 H 4 ρ = g/cm 3 fcc (?) Pd 3 H 4 ρ = 9.63 g/cm 3 Y. Fukai and H. Sugimoto, J. Phys.: Condens. Matter 19 (2007)

26 Formation of new phase cubic PdH Observations by Fukai: Contraction of lattice parameters was measured under high hydrogen pressures (2-5 GPa) and temperatures ( C) Pd Ar/H 2 plasma -100 V Pd, as deposited a 0 = Å intensity / cps as deposited 30 min 60 min 30 min: Pd (I), fcc a 0 = Å 60 min: Pd (I), fcc a 0 = Å Pd (II), fcc a 0 = 3.82 Å PdH 1.33, bcc a 0 = Å* 100 New phase at -100 V / 1 R.V. Baranova, Yu.P. Khodyrey, R.M. Imavov, S.A. Semiletov, Kristallografiya, 25 (1980) Y. Fukai et al. J. Alloys Comp. 313 (2000) 121

27 Temporal evolution of phase formation of PdH Substrate voltage -100 V min (100) PdH min 150 min 180 min 210 min Pd (I) fcc Pd (II)fcc (110) PdH 1.33 (111) PdH (degrees)

28 XR measurement and simulation of PdH 1.33 after 210 min Ar/H 2 plasma treatment at substrate potential -100 V fcc Pd 4 ρ = g/cm 3 fcc Pd 4 H 4 ρ = g/cm 3 Pd 3 H 4 ρ = 9.63 g/cm 3 bcc Pd 3 H 4 ρ = 9,9 g/cm 3

29 Conversion fcc Pd crystal structure into bcc PdH 1.33 (Pd 3 H 4 ) by plasma exposure c a z x y b Pd vac fcc V U = Å 3 Z Pd < 4? Pd 3 H 4 bcc 1 2*V U = 2 * Å 3 = Å 3 Z Pd = 3 Analog to Bain distortion: fcc bcc transformation shear (displacive) solid state change distortion is a compression of 28 % along [001] axes expansion of 10 % along the [110] and [110] axes 1 R.V. Baranova, Yu.P. Khodyrey, R.M. Imavov, S.A. Semiletov, Kristallografiya, 25 (1980) 1290

30 Annealing process, (in situ HT diffractometry): phase transformation PdH 1.33 Pd Vac Pd 3 H 4

31 Pitsch distortion Diffusionless phase transition Reversible diffusionless transition between low and high temperature phase Particles(atoms) move on distances < atomic distances There are strong orientation relationships between structure of the both phases. Fcc-bcc transformation by Pitsch distortion in 3D representation. (a) fcc cubic lattice lying with the (110) plane in vertical position, (b) Pitsch distortion with the x = [110] = [111] neutral line in horizontal position and marked by 0, (c) bcc crystal in a tetragonal frame after distortion, (d) same crystal in its basic cubic reference lattice (not well rendered y the perspective).

32 Outline (i) Motivation and experimental setup (ii) Incorporation of hydrogen (iii) Influence of temperature exposure (iv) Influence of substrate voltage and time of plasma treatment (v) Conclusions

33 Conclusions - Alternative way forming palladium hydride plasma exposure under vacuum conditions (Ar/H 2 ) - Formation of PdH x, P vac H x and PdH 1.33 phases Depends on substrate voltage 0 V : α-pdh and β-pdh - 50 V : β-pdh V : Pd vac H x, and phase transformation to PdH 1.33 (Pd 3 H 4 bcc) - Temperature behavior ß-PdH: > 300 C hydrogen desorption, lattice shrinking, strong increase of fcc Pd crystallinity Pd 3 H 4 : > 300 C phase transformation of cubic (bcc phase) back again to fcc Pd vac H x at 600 C (almost) pure fcc Pd vac H x phase exists > 600 C Pd 3 H 4 forms again, no hydrogen desorption

34 Acknowledgment Financial support for this work was provided by Deutsche Forschungsgemeinschaft (SFB TR24). We thank Dr. Klaus Ellmer (Helmholtz Centre Berlin) for preparation of the palladium films.

35 Thank you for your attention! Caspar David Friedrich Ansicht eines Hafens (painted )

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37 In-situ HTGIXD determination of lattice parameters change PdH 1.33 Pd vac 3,02 3,01 PdH ,79 3,78 Pd Vac lattice parameters /A 3,00 2,99 2, lattice parameters /A 3,77 3,76 3, ,97 RT temperature [ C] RT room temperature RT 3,74 temperature [ C] RT room temperature RT , time / min time / min Formation of fcc Desorption of hydrogen Lattice parameters vs. time substrate voltage -100 V

38 Phase transformation: palladium hydride bcc into fcc during annealing processes c a z x y b Pd 3 H 4 bcc 2 * V U = 2 * Å 3 = Å 3 T > 300 C T > 600 C Pd vac fcc V U = Å 3

39 Annealing process: phase transformation PdH 1.33 Pd Vac 800 bcc PdH 1.33 formation 700 c 600 z x a y temperature / C fcc Pd Vac formation b x PdH 1.33 = y Pd Vac y Pd vac

40 Bain distortion and the classical theories Bain distortion (fcc-bct-bcc transformation). The Pd and H atoms are in black and grey, respectively. The distortion is a compression of 20% along the [001] axis and expansion of 12% along the [110] and [10] axes. 1

41 In-situ HTGIXD, PdH1.33 (2) Pd vak Intensity / cps PdH 1, C C C room temperature after cooling /

42 In-situ HTGIXD lattice parameters vs. time Pd 3 H 4, substrate bias -100 V 3, ,01 PdH 1.33 lattice parameters /A 3,00 2,99 2, ,97 RT RT time / min