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Successful and Unsuccessful High-Pressure Attempts to Synthesize PdH(D)x > 1.0

Authors:

Abstract

This is a call to pursue the search for x > 1.0 (in PdHx) using high pressure (HP) synthesis, as well as a call to reproduce Pd-H SAVs (synthesized by HP) (and solve their crystal structure). N.B. : note that if you want to download the Poster in PDF format, go to the "More" tab and then click on "Download". Otherwise, if you download the Poster directly from the displayed picture (through a right click) then the downloaded file (in PNF format) will be of very poor resolution.
Successful and Unsuccessful
High-Pressure Attempts to Synthesize PdH(D)x > 1.0
N. Armanet,1* Z.M. Geballe,2 M. Somayazulu,3
E. MacA. Gray,4 D. Fruchart,5 N. Skryabina,6
D.S. dos Santos,7 P. Tripodi,8 M. Valat,1
F. De Guerville,1 M. Bonnard 1
1: i2-HMR -International Institute for Hydrogen Materials Research, France.
2: Earth and Planets Laboratory, Carnegie Institution of Washington, USA.
3: HPCAT, X-ray Science Division, Argonne National Laboratory, USA.
4: Queensland Micro-and Nanotechnology Centre, Griffith University, Australia.
5: Institut Néel, CNRS, France.
6 : Perm State University, Dept of Physics, Russia.
7 : Universidad Federal of Rio de Janeiro, Dpt PEEM, Brasil.
8 : Is Clean Air, Italy.
* : nicolas.armanet@i2-hmr.com
This is a call
to pursue the search
for x > 1.0 using
High Pressure synthesis !
and a call to reproduce
SAV as well !
Discussion
(a) Section ”Why PdH(D)x > 1.0 is so exciting?”
Since the 70s, the Pd-H system is known to be superconducting :Tc passes from ~ 0K at x = 0.75 to ~ 10K at x = 1.0 (see [2-8] in [1]).
HOWEVER, the past twenty years have seen two major events (i) and (ii) that might extend this “cold” superconductivity to RT
superconductivity (and maybe hotter).
(i) In the early 2000’s and in 2016, three different teams of investigators [2-13](Tripodi et al./Lipson et al./Gray et al.) published
superconducting transition temperatures (Tc) in the range 10-300K, via electrical resistance and magnetic measurements, with Pd-
H(D) samples hydrogenated electrolytically and in gas phase, at temperatures from RT to 300 °C, at pressures from ambient to 100
atm (thus, at light years away from the GPa range).Amongst these teams, achievement of x > 1.0 has been claimed, but without any
knowledge of the crystal structure of the superconducting phase(s).Based on their experimental Tc results and on Tc values from
literature up to 10 K, P. Tripodi et al. [3-4] constructed a simple model that predicts values of x and their corresponding Tc values :see
Fig. 1.For instance, Tc = 300 K might require x = 1.6.
(ii) Although not reproduced yet, all these results strongly resonate with the so-called "Super Hydride“ superconductors synthesized
since 2015 using high P / high Tin DACs (e.g. H2S, La-H, Y-H) where Tc values up to 300 K and even above have been found, and
where a common rule seems to be the higher the value of x, the higher the Tc value.
So, having in mind (i) and (ii),some recent attempts have been made to synthesize superstoichiometric Pd Hydrides using DACs.
Taking into account the many experimental results already present in the Pd-H literature for decades (e.g. via electrolysis, ion
implantation) claiming achievement of x > 1.0 (see e.g. a recent one using RT electrolysis [14]) the high-P synthesis of PdH(D)x at GPa
pressures (1 100 GPa) is thus expected to be successful, especially at high T(to bypass possible kinetic barriers).
BUT :see top left section “Negative results”.
(b) Section Negative results”
(i) Achievement of x = 1.0 at 2GPa at RT (up to at least 8GPa).Above 2GPa, the PdHx lattice parameter a(P) decreases monotically.
This should correspond to constant [H]:[Pd] ratio [1] and most likely to stoichiometric PdH, i.e. x = 1.0 [16,25]. This is supported by
complete reversibility of a(P) [1,24] and absence of adiscontinuity in a(P) [1,16,24-25]. In this vein, extrapolation to 0GPa yields aPdH
at ambient P. At x = 1.0, the simplest explanation is that 100 % of Osites are occupied ;howe ver, partial T-site occupancy has been
proposed [34]. That said, to conclusively pronounce on the H site occupancy, and on the real achievement of stoichiometric PdH,it is
still required to do Neutron Diffraction (ND) with Deuterium hence the term “apparent”. Theoretical papers that predict the P at
which x = 1.0 will be referred to in our paper for the MH 2022 proceedings.Finally, we note that PdH and PdD were synthesized in a
DAC below RT (i.e. 4 150K), 3.5 GPa, in 1989, during investigation of classic superconductivity (i.e. Tc < 11K) [35-36].
(ii) What exactly do “unsuccessful” (= negative) results actually mean to us ? Simply said, it’s when there is no indication tending to
show that x > 1.0 has been achieved.Typically, it’s the absence of any upward or downward discontinuity in the V(P) curve (like that
with PdHx in Fig. 3). A good example of a phase change with upward discontinuity (to a diHydride) can be seen in Fig. 2 in [24]. Also,
the absence of a continuous positive deviation from the compression trend implies no change in the stoichiometry. Besides, the
parallel between pure Pd V(P) and PdHx V(P) in Fig. 3 does not favour a phase change either.Finally, it has even been proposed that x
> 1.0 would be overlooked in high P XRD measurements since a(P) for x > 1.0 can be lower than that at x < 1.0 (see Fig. 2 in [14])
hence, a further reason to study high Psynthesis of PdHx using ND rather than XRD !
(c) Section “Positive results” (SAVs)
Pd-H SAVs need to be reproduced (using high P / high T). Synthesis with Deuterium (to facilitate ND) has not been done yet. The two
proposed ordered structures (and thus the x = 1.33 value) need to be confirmed by ND still not done yet in 2022! A further big mission
for ND (and for any other adopted analysis) is : but where in fact do H (or D) reside in the proposed structures ? in Osites ?in Tsites ?in
Pd vacancies ? Such a question is very exciting in regard to the fact that, for instance, as pointed out by Antonov et al.(see pp. 2, 9 in
[38]), partial T-site occupancy in Pd monoHydride should have astrong impact on its optical vibrations and thus on the occurrence of
high T superconductivity such as that found by Gray et al. [12] (Tc = 50 K).
(d) Possible reasons for failure to achieve x > 1.0 (with hints for future attempts)
Considering possible non-SAV overstoichiometric structures : a naive reason for failure is maybe simply the use of pressures too low for
a phase change to occur and/or a bad combination of P and T. See the Table to find out what has been already tried.
If one considers the SAV results as the most credible overstoichiometric Hydrides (so far) then the question becomes :did the
unsuccessful results use the very same experimental conditions that effectively led to SAV synthesis ?Clearly :no, as can be seen in the
Table opposite. None of the “unsuccessful” teams used the SAV conditions of T, P, duration of heating.Note that our paper for MH-2022
proceedings will cite various theoretical papers predicting overstoichiometric Pd Hydrides (Deuterides) (SAV and nonSAV). Such papers
should also be helpful for future attempts.
because the Pd-H(D) system
is a credible candidate
for room temperature superconductivity,
as indicated by the Fig. 1 below ;
see (a) in Discussion to find out more !
Why PdH(D)x > 1.0 is so exciting?
Fig. 1
References :[1] : Z.M. Geballe et al., PRB, 103 (2021)024515.[2] : P. Tripodi et al., Physica C, 388 (2003)571.[3] : P. Tripodi et al., Physica C, 408 (2004)350.[4] : P. Tripodi et al., Braz.J.Phys., 34 (2004)1177.[5] : P. Tripodi et al., J. Phys. : Conf.Ser., 43 (2006)690.
[6] : P. Tripodi et al., Int. J. Mod. Phys.B, 21 (2007)3343.[7] : F. Celani et al., Proceedings of the 6th International Conference on Cold Fusion (ICCF6), Vol. 1, p. 228,1996.[8] : A.G. Lipson et al., Phys.Lett. A, 339 (2005)414.[9] : A.G. Lipson et al., Phys.Rev.B, 72
(2005)212507.[10]: A.G. Lipson et al., J. Exp.Theor.Phys., 103 (2006)385.[11]: C.H. Castano Giraldo,Master Thesis, University of Illinois at Urbana-Champaign, USA, 2002.[12]: H.M. Syed et al., arXiv:1608,01774,2016.[13]: H.M. Syed,Ph.D. Thesis, Griffith
University, Australia, 2016.[14]: N. Fukumuro et al., J. Alloys Compd., 825 (2020)153830.[15]: S.A. Steel, Ph.D. Thesis, University of Salford Manchester, UK, 2018.[16]: B. Guigue et al., J. Appl.Phys., 127 (2020)075901.[17]: B. Guigue et al., ESRF Report,
Experiment HC-3382,2018.[18]: B. Guigue,Ph.D. Thesis,Universi PSL Paris, France, 2019 -in French.[19]:D.K. Ross et al., PRB, 58 (1998)2591.[20]: V.E. Antonov et al., Int.J.H.Energ., 42 (2017)22454.[21]: V.E. Antonov, N. Armanet, B.M. Bulychev, V.K.
Fedotov, V.I. Kulakov, D.V. Matveev, I.A. Sholin, V.Y. Zuykova,Vegard’s Law for the solid hydrogen solutions in Pd and Pd-Au alloys resulting from high-temperature high-pressure hydrogenation,PPT presented at the MH-2016 Conference in Switzerland,2016.[22]:
V.E. Antonov, N. Armanet, B.M. Bulychev, V.K. Fedotov, V.I. Kulakov, M.A. Kuzovnikov, I.A. Sholin, V.Y. Zuykova,Hydrogen-Induced Volume Expansion of fcc Pd-Cu Alloys,Poster presented at the MH-2018 Conference in China, 2018.[23]:The work [21-22]is in
preparation for publication.[24]: M.A. Kuzovnikov et al., Int.J.H.Energ., 42 (2017)340.[25]: K. Brownsberger et al., J. Phys.Chem.C, 121 (2017)27327.[26]: T. Fedotenko et al., Rev.Sci.Instrum., 90 (2019)104501.[27]: T. Fedotenko et al., J. Alloys Compd., 844
(2020)156179.[28]: T. Fedotenko,Ph.D. Thesis, University of Bayreuth, Germany, 2021.[29]: Y. Fukai et al., Jpn.J.Appl.Phys., 32 (1993) L1256.[30]: Y. Fukai et al., Phys.Rev.Lett., 73 (1994)1640.[31]:D.S. dos Santos et al., J. Alloys Compd., 291 (1999) L1. [32]:
S. Miraglia et al., J. Alloys Compd., 317-318 (2001)77.[33]: V. Azambuja et al., J. Alloys and Compd., 404-406 (2005)77.[34]: S.S. Setayandeh et al., J. Alloys and Compd., 864 (2021)158713.[35]: H. Hemmes et al., PRB, 39 (1989)4110.[36]: H. Hemmes et al., Rev.
Sci.Instrum., 60 (1989)474.[37]: Y. Fukai et al., J. Phys. : Condens.Matter,19 (2007)436201.[38]: V.E. Antonov et al., Phys.Rev. Mat., 3 (2019)113604.[39]: I.F. Silvera et al., PRB, 42 (1990)9143.[40]: B. Baranowski et al., J. Less-Common Met., 158 (1990)347.
Acknowledgements are due to (i) A.K. Mish ra, M. Ahart, R.J. Hemley (ref. [1]), and to (ii) S.S. Setay andeh, T. Gould, A. Vaez, K. McLennan (ref. [34]). N.A. g ratefully acknowledges V.E. Antonov and M.A. Kuzov nikov
for past discussions about ref. [25 ]. N.A. also warmly thanks Driss Sadoun and Lola S izaire for their inestimable ;) assistance during the very first s teps of the 1st draft of this Poster on 14th Oct.2022 as well as for
the wonderful birthday week-end on 14th-16th Oct .2022 at Marseille (France) together with Anne-Claire Swale , Aleksandra Malkova,Samir Sadoun,Laetit ia Weinhard,Boris Brinkma nn,Hervé Bogreau Holy
Ravalason was unfortunately ill.Our very big ap éro pic-nic at the Plage des Catalans” will never be forgotten ;) ;)
This Poster is a literature review
of experimental results from independent teams,
and from our own investigations.
Positive but uncertain claims of x > 1.0
Fig. 7 : same as in Fig. 2, where
Brownsberger et al. [25]’s lowest
PXRD data (~ 8GPa) is estimated
to yield x = 1.2 according to [1].
Context :
«Cold Fusion »
1989 -1990
(except Brownsberger)
Brownsberger et al.
~ 8 GPa, RT
Silvera et al.
4-10 GPa, 4-400K
Baranowski et al.
3.1 GPa, RT
Fig. 8 : DAC set-up [39]where
Deuterium (white) and Pd (black,
see red arrows) are clamped
between the diamonds.[D]/[Pd]
= 1.34 +/- 0.01.Note the
similarity of this 1.34 with the x =
1.33 with SAV (pure chance?).
Fig. 9 : Example of cylinder-
piston combination used by
Baranowski and colleagues, with
in-situ measurement of the
sample electrical resistance R.
[D]/[Pd] estimated to be > 1.0.
Fig. 7 : Brownsberger et al. [25]found alattice parameter value for PdH (extrapolated
to ambient pressure) big enough to be interpreted to be overstoichiometric (e.g.
belonging to PdH2). However, the absence of any discontinuity in their V(P) does not
favour such aphase change.
Fig. 8 : XRD was not used here.Silvera et al.[39](1990)estimated xfrom moles of D2
and of Pd.Moles of D2are calculated via dV between starting and ending volume of D2,
yielding the absorbed Deuterium within Pd sample.The authors excluded the possibility
of D2leaks, which would automatically overestimate their xvalue.
Fig. 9 : XRD was not used here.Baranowski et al.[40](1990)estimated the
achievement of x > 1.0 via changes of slope in their measured R/R0(P) (with R0 the Rof
pure Pd).
Negative results
(i.e. x = 1.0 only, and no phase change)
Apparent achievement
of x = 1.0 at RT at P = 2 GPa
No apparent phase change
even up to 100 GPa
at RT and > 1300 K
Fig. 2 : PdHx Room Temperature
behaviour, a(P) and x(P) plots taken
from [1]. For PdDx, see Fig. 3 and 6 in
[16].
Fig. 3 : PdHx a(P) behaviour at room
temperature and after laser heating
sequences plot taken from [16]. For
PdDx, see Fig. 4 in [16]. Note the parallel
between pure Pd and PdHx.This
behaviour tends to show that PdH is
simply step by step compressed asPis
increased up to 1 Mbar (100 GPa), with
no phase transition.
Fig. 2 : to find out more about the achievement of x = 1.0 at P < 8 GPa at RT (and
things like Ovs Tsites) see (b) in Discussion section.
Fig. 3 : to the best of our knowledge, and despite the use of DACs (able to explore the
range 1 100 GPa) in the period 2017-2020,no one could detect any apparent
indications of superstoichiometric Pd Hydrides (Deuterides) at Pup to 1Mbar and Tfrom
RT to 2000 K, among the 6independent teams of experimenters [1,16-19,21-28]. See the
Table for details about the experimental conditions.
See the Table for details
about experimental conditions used by all the
unsuccessful attempts (from 6 teams of investigators)
Stoichiometric PdH,
NaCl structure,
with H in O-sites,
after [15] p. 15.
Pd
H
Context :
«SuperConductor
SuperHydrides »
2015 -2021
(except Antonov)
2020
Positive results
(i.e. SAV, with x = 1.33)
Achievement of superstoichiometric Hydrides deduced from detection
of superlattice lines at 3 5 GPa and 350 800 °C
°C
Fig. 4 : PdHx a(t) behaviour at 5
GPa plot taken from [29].
Phase separation into A (PdH)
and B (Simple Cubic Pd3VacH4).
A
A
A
B
B
Fig. 5 : XRD pattern of PdHx at 500 °C
and a H2pressure of 5GPa, after
holding at 800 °C for 3.5 h plot taken
from [30]. Phase separation into A
(PdH) and B (Simple Cubic Pd3VacH4).
Fig. 6 : SEM image of
micrometric pores in
PdHx sample, as a result
of vacuum annealing at
800 °C for 1h, after
holding at 800 °C for 5 h
under 3.5 GPa H2plot
taken from [32].
Pd-H SAVs are defected Hydrides, i.e. exotic crystals with Super Abundant Vacancies (SAV) in place of Pd
atoms as depicted above [37]with the example of the SAV Simple Cubic (SC) crystal, designated “B”. N.B. :
production of Pd vacancies at those “low temperatures is abnormal.
So far, two ordered SAV phases have been detected by XRD and ascribed as Tetragonal (PdH1.33)(not
shown) and SC (Pd3VacH4) (shown in Figs 4 and 5), the last being presumably a high-temperature modification
of the former, both with a reduced lattice parameter (compared to PdH) [29-33].
The proposed crystal structures (with x = 1.33)refer only to the Pd lattice since XRD is blind to Hatoms.
These SAV phases are stable once ambient conditions (of P and T) are recovered : a remarkable feature!
Fig. 6 : their destabilization leads to (Pd) vacancies coalescing into stable pores.
First widely known experimental results are due to Fukai et al. (1993-1994)[29-30], followed so far by only
one replication by Fruchart and dos Santos et al. (1999-2005)[31-33].
To find out more about Pd SAVs, see (c) in Discussion.
Pd
H
PdH,
NaCl type
A
Pd3VacH4,
Cu3Au type
B
Context :
« SAV »
1993 -2005
See the Table for details
about the experimental conditions
DAC
Diamond Anvil Cell
Picture taken from :
http://sites.co loradocollege.e du
/pcervantes/fac ilities/
https://en.wikipedia.org/wiki/Once_Upon_a_Time..._Life
Example of another type of HighP cell :
Paris Edinburgh Press (PE press)
Picture taken from slide 3 in Y. Le Godec et al.’s PPT,
see : https://www.esrf.fr/home/events/conferences/2019/
school-on-high-pressure-techniques/
lecturers-abstracts-and-presentations.html
PdH1.0
Our knowledge on PdH(D)x > 1.0 (synthesized at High P) has
recently been improved, but does still remain close to
zero !If one wants to get RT superconductivity one day
with this system, it ’s time to act !
Moreover, the effective achievement of x = 1.0 is still uncertain ... as well as the
interstitials location (at x = 1.0).
Despite afew recent (2017-2021)High Pattempts (up to 1Mbar) in the
“SuperConductors SuperHydrides” context, we still don’t know whether x > 1.0
in PdH(D)x is amyth or not.Although some positive (but uncertain) High P
results claimed x > 1.0 (in the 1989-1990 “Cold Fusion” context), the Pd-H SAV
phases (1993-2005)are so far the more credible overstoichiometric candidates.
They however need to be reproduced and their crystal structures solved by
neutron diffraction (especially to confirm x = 1.33). Besides, the lack of x > 1.0
results using current DACs is very surprising in relation to the many published
results claiming overstoichiometry in Pd-H(D) using techniques like electrolysis.
Since three different teams of investigators claimed the achievement of
superconductivity within the range Tc =10-300Kwith Pd-H(D) (2003-2016), it is
exciting to find out whether their superconductive phase(s) has x > 1.0 (or not)
and whether it is a SAV phase (or not).
in Summary :
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