Polyhydride
{{short description|Chemical compound}}
{{For|the reducing agent known as Superhydride|Lithium triethylborohydride}}
A polyhydride or superhydride is a compound that contains an abnormally large amount of hydrogen. This can be described as high hydrogen stoichiometry. Examples include iron pentahydride {{chem2|FeH5}}, {{chem2|LiH6}}, and {{chem2|LiH7}}. By contrast, the more well known lithium hydride only has one hydrogen atom.{{cite journal|last1=Pépin|first1=C. M.|last2=Geneste|first2=G.|last3=Dewaele|first3=A.|last4=Mezouar|first4=M.|last5=Loubeyre|first5=P.|title=Synthesis of FeH5 : A layered structure with atomic hydrogen slabs|journal=Science|date=27 July 2017|volume=357|issue=6349|pages=382–385|doi=10.1126/science.aan0961|pmid=28751605|bibcode=2017Sci...357..382P|doi-access=free}}
Polyhydrides are only known to be stable under high pressure.
Polyhydrides are important because they can form substances with a very high density of hydrogen. They may resemble the elusive metallic hydrogen, but can be made under lower pressures. One possibility is that they could be superconductors. Hydrogen sulfide under high pressures forms {{chem2|SH3}} units, and can be a superconductor at {{convert|203|K|C}} and a pressure of 1.5 million atmospheres (152 GPa).
Structures
File:Sodium pentahydride unit cell.jpg
The polyhydrides of alkaline earth and alkali metals contain cage structures. Also hydrogen may be clustered into {{chem2|H−}}, {{chem2|H3−}}, or {{chem2|H2}} units. Polyhydrides of transition metals may have the hydrogen atoms arranged around the metal atom. Computations suggest that increasing hydrogen levels will reduce the dimensionality of the metal arrangement, so that layers form separated by hydrogen sheets. The {{chem2|H3−}} substructure is linear.{{cite journal|last1=Struzhkin|first1=Viktor V.|last2=Kim|first2=Duck Young|last3=Stavrou|first3=Elissaios|last4=Muramatsu|first4=Takaki|last5=Mao|first5=Ho-kwang|last6=Pickard|first6=Chris J.|last7=Needs|first7=Richard J.|last8=Prakapenka|first8=Vitali B.|last9=Goncharov|first9=Alexander F.|title=Synthesis of sodium polyhydrides at high pressures|journal=Nature Communications|date=28 July 2016|volume=7|pages=12267|doi=10.1038/ncomms12267|pmid=27464650|pmc=4974473|bibcode=2016NatCo...712267S}}
Trihydrogen cation would form triangular structures in the hypothetical {{chem2|H5Cl}}.
Compounds
When sodium hydride is compressed with hydrogen, {{chem2|NaH3}} and {{chem2|NaH7}} form. These are formed at 30 GPa and 2,100 K.
Heating and compressing a metal with ammonia borane avoids using bulky hydrogen, and produces boron nitride as a decomposition product in addition to the polyhydride.
| class="wikitable"
!formula !name !temperature °C !pressure GPa !crystal structure !space group !a Å !b !c !β !cell volume !formulae per unit cell !Tc K !Comment !refs |
| {{chem2|LiH2}}
|lithium dihydride |27 |130 | | | | | | | | | | |
| {{chem2|LiH6}}
|Lithium hexahydride | | | | | | | | | | | | |
| {{chem2|LiH7}}
|Lithium heptahydride | | | | | | | | | | | | |
| {{chem2|NaH3}}
|sodium trihydride | | |orthorhombic |Cmcm |3.332 Å |6.354 Å |4.142 Å |90 |87.69 |4 | | |
| {{chem2|NaH7}}
|sodium heptahydride | | |monoclinic |Cc |6.99 |3.597 |5.541 |69.465 |130.5 | | | |
| {{chem2|CaH_{x} |
|
|500
|22
|double hexagon
|
|
|
|
|
|
|
|
|
|-
|{{chem2|CaH_{x}|}}
|
|600
|121
|
|
|
|
|
|
|
|
|
|
|-
|RbH9−x
|
|
|10
|
|Cccm
|
|
|
|
|
|
|
|
|-
|RbH9−x
|
|
|
|
|Cm
|
|
|
|
|
|
|
|
|
|-
|{{chem2|SrH6}}
|
|
|
|pseudo cubic
|Pm{{overbar|3}}m
|
|
|
|
|
|
|
|semiconductor
metallize > 220 GPa
|-
|{{chem2|Sr3H13}}
|
|
|
|
|C2/m
|
|
|
|
|
|
|
|
|-
|{{chem2|SrH22}}
|
|
|138
|triclinic
|P1
|
|
|
|
|
|
|
|
|-
|{{chem2|BaH12}}
|Barium dodecahydride
|
|75
|pseudo cubic
|
|5.43
|5.41
|5.37
|
|39.48
|
|20K
|
|{{Cite web|url=https://www.researchgate.net/publication/340930295|title=High-Pressure Synthesis of Barium Superhydrides: Pseudocubic BaH12|last=chen|first=Wuhao|date=April 2020|website=ResearchGate|language=en|access-date=2020-04-28}}{{cite journal |last1=Chen |first1=Wuhao |last2=Semenok |first2=Dmitrii V. |last3=Kvashnin |first3=Alexander G. |last4=Huang |first4=Xiaoli |last5=Kruglov |first5=Ivan A. |last6=Galasso |first6=Michele |last7=Song |first7=Hao |last8=Duan |first8=Defang |last9=Goncharov |first9=Alexander F. |last10=Prakapenka |first10=Vitali B. |last11=Oganov |first11=Artem R. |last12=Cui |first12=Tian |title=Synthesis of molecular metallic barium superhydride: pseudocubic BaH12 |journal=Nature Communications |date=December 2021 |volume=12 |issue=1 |pages=273 |doi=10.1038/s41467-020-20103-5|pmid=33431840 |pmc=7801595 |arxiv=2004.12294 |bibcode=2021NatCo..12..273C |doi-access=free}}
|-
|{{chem2|FeH5}}
|1200
|66
|tetragonal
|I4/mmm
|
|
|
|
|
|
|
|
|-
|{{chem2|H3S}}
|25
|150
|cubic
|Im{{overbar|3}}m
|
|
|
|
|
|
|203K
|
|-
|{{chem2|H3Se}}
|Selenium trihydride
|
|10
|
|
|
|
|
|
|
|
|
|
|-
|{{chem2|YH4}}
|yttrium tetrahydride
|700
|160
|
|I4/mmm
|
|
|
|
|
|
|
|
|-
|{{chem2|YH6}}
|yttrium hexahydride
|700
|160
|
|Im-3m
|
|
|
|
|
|
|224
|
|{{cite journal|last1=Troyan|first1=I. A.|last2=Semenok|first2=D. V.|last3=Kvashnin|first3=A. G.|last4=Ivanova|first4=A. G.|last5=Prakapenka|first5=V. B.|last6=Greenberg|first6=E.|last7=Gavriliuk|first7=A. G.|last8=Lyubutin|first8=I. S.|last9=Struzhkin|first9=V. V.|last10=Oganov|first10=A. R.|title=Anomalous High-Temperature Superconductivity in YH 6|journal=Advanced Materials|year=2021|volume=33|issue=15|pages=e2006832|doi=10.1002/adma.202006832 |issn=0935-9648|pmid=33751670|language=en|arxiv=1908.01534|bibcode=2021AdM....3306832T |s2cid=219636252}}{{cite journal |last1=Troyan |first1=Ivan A. |last2=Semenok |first2=Dmitrii V. |last3=Kvashnin |first3=Alexander G. |last4=Sadakov |first4=Andrey V. |last5=Sobolevskiy |first5=Oleg A. |last6=Pudalov |first6=Vladimir M. |last7=Ivanova |first7=Anna G. |last8=Prakapenka |first8=Vitali B. |last9=Greenberg |first9=Eran |last10=Gavriliuk |first10=Alexander G. |last11=Lyubutin |first11=Igor S. |last12=Struzhkin |first12=Viktor V. |last13=Bergara |first13=Aitor |last14=Errea |first14=Ion |last15=Bianco |first15=Raffaello |last16=Calandra |first16=Matteo |last17=Mauri |first17=Francesco |last18=Monacelli |first18=Lorenzo |last19=Akashi |first19=Ryosuke |last20=Oganov |first20=Artem R. |title=Anomalous High-Temperature Superconductivity in YH 6 |journal=Advanced Materials |date=10 March 2021 |volume=33 |issue=15 |pages=2006832 |doi=10.1002/adma.202006832|issn=0935-9648|pmid=33751670 |arxiv=1908.01534 |bibcode=2021AdM....3306832T |s2cid=219636252}}
|-
|{{chem2|YH9}}
|400
|237
|
|P63/mmc
|
|
|
|
|
|
|243
|
|-
|CsH7
|
|
|
|tetragonal
|P4/nmm
|
|
|
|
|
|
|
|
|-
|CsH15+x
|
|
|
|triclinic
|P1
|
|
|
|
|
|
|
|
|-
|{{chem2|LaH10}}
|1000
|170
|cubic
|Fm{{overbar|3}}m
|5.09
|5.09
|5.09
|
|132
|4
|250K
|
|{{cite journal|last1=Geballe|first1=Zachary M.|last2=Liu|first2=Hanyu|last3=Mishra|first3=Ajay K.|last4=Ahart|first4=Muhtar|last5=Somayazulu|first5=Maddury|last6=Meng|first6=Yue|last7=Baldini|first7=Maria|last8=Hemley|first8=Russell J.|title=Synthesis and Stability of Lanthanum Superhydrides|journal=Angewandte Chemie International Edition|date=15 January 2018|volume=57|issue=3|pages=688–692|doi=10.1002/anie.201709970|pmid=29193506|bibcode=2018APS..MARX38010G|doi-access=free}}{{cite journal |last1=Drozdov |first1=A. P. |last2=Kong |first2=P. P. |last3=Minkov |first3=V. S. |last4=Besedin |first4=S. P. |last5=Kuzovnikov |first5=M. A. |last6=Mozaffari |first6=S. |last7=Balicas |first7=L. |last8=Balakirev |first8=F. F. |last9=Graf |first9=D. E. |last10=Prakapenka |first10=V. B. |last11=Greenberg |first11=E. |last12=Knyazev |first12=D. A. |last13=Tkacz |first13=M. |last14=Eremets |first14=M. I. |title=Superconductivity at 250 K in lanthanum hydride under high pressures |journal=Nature |date=22 May 2019 |volume=569 |issue=7757 |pages=528–531 |doi=10.1038/s41586-019-1201-8|pmid=31118520 |arxiv=1812.01561 |bibcode=2019Natur.569..528D |s2cid=119231000}}
|-
|{{chem2|LaH10}}
|25
|121
|Hexagonal
|R{{overbar|3}}m
|3.67
|3.67
|8.83
|
|
|1
|
|
|-
|{{chem2|LaD11}}
|2150
|130-160
|Tetragonal
|P4/nmm
|
|
|
|
|
|
|168
|
|-
|{{chem2|LaH12}}
|
|
|Cubic
|
|
|
|
|
|
|
|insulating
|
|-
|{{chem2|LaH7}}
|Lanthanum heptahydride
|25
|109
|monoclinic
|C2/m
|6.44
|3.8
|3.69
|135
|63.9
|2
|
|
|-
|{{chem2|CeH9}}
|Cerium nonahydride
|
|93
|hexagonal
|P63/mmc
|3.711
|
|5.543
|
|33.053
|
|100K
|
|-
|{{chem2|CeH10}}
|Cerium decahydride
|
|
|
|Fm{{overbar|3}}m
|
|
|
|
|
|
|115K
|
|-
|{{chem2|PrH9}}
|Praseodymium nonahydride
|
|90-140
|
|P63/mmc
|3.60
|
|5.47
|
|61.5
|
|55K 9K
|
|{{Cite journal|last1=Zhou|first1=Di|last2=Semenok|first2=Dmitrii|last3=Defang Duan|last4=Xie|first4=Hui|last5=Xiaoli Huang|last6=Wuhao Chen|last7=Li|first7=Xin|last8=Bingbing Liu|last9=Oganov|first9=Artem R|date=2019|title=Superconducting Praseodymium Superhydrides|journal= Science Advances|volume=6|issue=9|pages=eaax6849|language=en|doi=10.1126/sciadv.aax6849|pmid=32158937|pmc=7048426|arxiv=1904.06643|bibcode=2020SciA....6.6849Z}}{{Cite journal|last1=Zhou|first1=Di|last2=Semenok|first2=Dmitrii V.|last3=Duan|first3=Defang|last4=Xie|first4=Hui|last5=Chen|first5=Wuhao|last6=Huang|first6=Xiaoli|last7=Li|first7=Xin|last8=Liu|first8=Bingbing|last9=Oganov|first9=Artem R.|last10=Cui|first10=Tian|date=February 2020|title=Superconducting praseodymium superhydrides|url= |journal=Science Advances|language=en|volume=6|issue=9|pages=eaax6849|doi=10.1126/sciadv.aax6849|issn=2375-2548|pmc=7048426|pmid=32158937|arxiv=1904.06643|bibcode=2020SciA....6.6849Z}}
|-
|{{chem2|PrH9}}
|Praseodymium nonahydride
|
|120
|
|F43m
|4.98
|
|
|
|124
|
|69K
|
|-
|{{chem2|NdH4}}
|Neodymium tetrahydride
|
|85-135
|tetragonal
|I4/mmm
|2.8234
|
|5,7808
|
|
|
|
|
|-
|{{chem2|NdH7}}
|Neodymium heptahydride
|
|85-135
|monoclinic
|C2/c
|3.3177
|6.252
|5.707
|89.354
|
|
|
|
|-
|{{chem2|NdH9}}
|Neodymium nonahydride
|
|110-130
|hexagonal
|P63/mmc
|3.458
|
|5.935
|
|
|
|
|
|-
|{{chem2|EuH4}}
|
|
|50-130
|
|I4/mmm
|
|
|
|
|
|
|
|
|-
|{{chem2|Eu8H46}}
|
|1600
|130
|cubic
|Pm{{overbar|3}}n
|5.865
|
|
|
|
|
|
|
|-
|{{chem2|EuH9}}
|Europium nonahydride
|
|86-130
|cubic
|F{{overbar|4}}3m
|
|
|
|
|
|
|
|
|-
|{{chem2|EuH9}}
|Europium nonahydride
|
|>130
|hexagonal
|P63/mmc
|
|
|
|
|
|
|
|
|-
|{{chem2|ThH4}}
|Thorium tetrahydride
|
|86
|
|I4/mmm
|2.903
|
|4.421
|
|57.23
|2
|
|
|-
|{{chem2|ThH4}}
|Thorium tetrahydride
|
|88
|trigonal
|P321
|5.500
|
|3.29
|
|86.18
|
|
|
|-
|{{chem2|ThH4}}
|Thorium tetrahydride
|
|
|orthorhombic
|Fmmm
|
|
|
|
|
|
|
|
|-
|{{chem2|ThH6}}
|Thorium hexahydride
|
|86-104
|
|Cmc21
|
|
|
|
|32.36
|
|
|
|-
|{{chem2|ThH9}}
|Thorium nonahydride
|2100
|152
|hexagonal
|P63/mmc
|3.713
|
|5.541
|
|66.20
|
|
|
|-
|{{chem2|ThH10}}
|Thorium decahydride
|1800
|85-185
|cubic
|Fm{{overbar|3}}m
|5.29
|
|
|
|148.0
|
|161
|
|-
|{{chem2|ThH10}}
|Thorium decahydride
|
|<85
|
|Immm
|5.304
|3.287
|3.647
|
|74.03
|
|
|
|-
|{{chem2|UH7}}
|Uranium heptahydride
|2000
|63
|fcc
|P63/mmc
|
|
|
|
|
|
|
|
|-
|{{chem2|UH8}}
|Uranium octahydride
|300
|1-55
|fcc
|Fm{{overbar|3}}m
|
|
|
|
|
|
|
|
|-
|{{chem2|UH9}}
|Uranium nonahydride
|
|40-55
|fcc
|P63/mmc
|
|
|
|
|
|
|
|
|}
=Predicted=
Using computational chemistry many other polyhydrides are predicted, including {{chem2|LiH8}},{{cite journal|last1=Duan|first1=Defang|last2=Liu|first2=Yunxian|last3=Ma|first3=Yanbin|last4=Shao|first4=Ziji|last5=Liu|first5=Bingbing|last6=Cui|first6=Tian|title=Structure and superconductivity of hydrides at high pressures|journal=National Science Review|volume=4|date=28 April 2016|pages=121–135|doi=10.1093/nsr/nww029|doi-access=free}}
{{chem2|LiH9}},{{cite journal|last1=Chen|first1=Yangmei|last2=Geng|first2=Hua Y.|last3=Yan|first3=Xiaozhen|last4=Sun|first4=Yi|last5=Wu|first5=Qiang|last6=Chen|first6=Xiangrong|title=Prediction of Stable Ground-State Lithium Polyhydrides under High Pressures|journal=Inorganic Chemistry|volume=56|issue=7|pages=3867–3874|doi=10.1021/acs.inorgchem.6b02709|pmid=28318270|year=2017|arxiv=1705.04199|s2cid=21976165}} {{chem2|LiH10}}, {{chem2|CsH3}},{{cite journal|last1=Shamp|first1=Andrew|last2=Hooper|first2=James|last3=Zurek|first3=Eva|date=3 September 2012|title=Compressed Cesium Polyhydrides: Cs+ Sublattices and H3- Three-Connected Nets|journal=Inorganic Chemistry|volume=51|issue=17|pages=9333–9342|doi=10.1021/ic301045v|pmid=22897718}} {{chem2|KH5}}, {{chem2|RbH5}}, {{chem2|RbH9}}, {{chem2|NaH9}}, {{chem2|BaH6}},{{cite journal|last1=Zurek|first1=Eva|date=6 June 2016|title=Hydrides of the Alkali Metals and Alkaline Earth Metals Under Pressure|journal=Comments on Inorganic Chemistry|volume=37|issue=2|pages=78–98|doi=10.1080/02603594.2016.1196679|s2cid=99251100}} {{chem2|CaH6}},{{cite journal|last1=Wang|first1=H.|last2=Tse|first2=J. S.|last3=Tanaka|first3=K.|last4=Iitaka|first4=T.|last5=Ma|first5=Y.|title=Superconductive sodalite-like clathrate calcium hydride at high pressures|journal=Proceedings of the National Academy of Sciences|date=6 April 2012|volume=109|issue=17|pages=6463–6466|doi=10.1073/pnas.1118168109|pmid=22492976|pmc=3340045|bibcode=2012PNAS..109.6463W|arxiv=1203.0263|doi-access=free}} {{chem2|MgH4}}, {{chem2|MgH12}}, {{chem2|MgH16}},{{cite journal|last1=Lonie|first1=David C.|last2=Hooper|first2=James|last3=Altintas|first3=Bahadir|last4=Zurek|first4=Eva|title=Metallization of magnesium polyhydrides under pressure|journal=Physical Review B|date=19 February 2013|volume=87|issue=5|pages=054107|doi=10.1103/PhysRevB.87.054107|bibcode=2013PhRvB..87e4107L|arxiv=1301.4750|s2cid=85453835}} {{chem2|SrH4}},{{cite journal|last1=Hooper|first1=James|last2=Terpstra|first2=Tyson|last3=Shamp|first3=Andrew|last4=Zurek|first4=Eva|title=Composition and Constitution of Compressed Strontium Polyhydrides|journal=The Journal of Physical Chemistry C|date=27 March 2014|volume=118|issue=12|pages=6433–6447|doi=10.1021/jp4125342}} {{chem2|SrH10}}, {{chem2|SrH12}}, {{chem2|ScH4}}, {{chem2|ScH6}}, {{chem2|ScH8}},{{Cite journal|last=Qian|first=Shifeng|date=2017|title=Theoretical study of stability and superconductivity of|journal=Physical Review B|volume=96|issue=9|pages=094513|doi=10.1103/physrevb.96.094513|bibcode=2017PhRvB..96i4513Q}} {{chem2|YH4}} and {{chem2|YH6}},{{cite journal|last1=Li|first1=Yinwei|last2=Hao|first2=Jian|last3=Liu|first3=Hanyu|last4=Tse|first4=John S.|last5=Wang|first5=Yanchao|last6=Ma|first6=Yanming|date=5 May 2015|title=Pressure-stabilized superconductive yttrium hydrides|journal=Scientific Reports|volume=5|issue=1|pages=9948|bibcode=2015NatSR...5.9948L|doi=10.1038/srep09948|pmid=25942452|pmc=4419593}} {{chem2|YH24}}, {{chem2|LaH8}}, {{chem2|LaH10}},{{cite journal|last1=Liu|first1=Hanyu|last2=Naumov|first2=Ivan I.|last3=Hoffmann|first3=Roald|last4=Ashcroft|first4=N. W.|last5=Hemley|first5=Russell J.|title=Potential high-Tc superconducting lanthanum and yttrium hydrides at high pressure|journal=Proceedings of the National Academy of Sciences|date=3 July 2017|volume=114|issue=27|pages=6990–6995|doi=10.1073/pnas.1704505114|pmid=28630301|pmc=5502634|bibcode=2017PNAS..114.6990L|doi-access=free}} {{chem2|YH9}}, {{chem2|LaH11}}, {{chem2|CeH8}}, {{chem2|CeH9}}, {{chem2|CeH10}},{{cite journal |last1=Tsuppayakorn-aek |first1=Prutthipong |last2=Pinsook |first2=Udomsilp |last3=Luo |first3=Wei |last4=Ahuja |first4=Rajeev |last5=Bovornratanaraks |first5=Thiti |title=Superconductivity of Superhydride CeH10 under High Pressure |journal=Materials Research Express |date=12 August 2020 |volume=7 |issue=8 |page=086001 |doi=10.1088/2053-1591/ababc2 |bibcode=2020MRE.....7h6001T |s2cid=225379054 |doi-access=free }} {{chem2|PrH8}}, {{chem2|PrH9}}, {{chem2|ThH6}}, {{chem2|ThH7}} and {{chem2|ThH10}},{{cite news|last1=Kvashnin|first1=Alexander G.|last2=Semenok|first2=Dmitry V.|last3=Kruglov|first3=Ivan A.|last4=Oganov|first4=Artem R.|title=High-Temperature Superconductivity in Th-H System at Pressure Conditions|arxiv=1711.00278|date=November 2017|bibcode=|doi=10.1021/acsami.8b17100}} {{chem2|U2H13}}, {{chem2|UH7}}, {{chem2|UH8}}, {{chem2|UH9}},{{cite arXiv|last1=Kruglov|first1=Ivan A.|last2=Kvashnin|first2=Alexander G.|last3=Goncharov|first3=Alexander F.|last4=Oganov|first4=Artem R.|last5=Lobanov|first5=Sergey|last6=Holtgrewe|first6=Nicholas|last7=Yanilkin|first7=Alexey V.|title=High-temperature superconductivity of uranium hydrides at near-ambient conditions|eprint=1708.05251|date=17 August 2017|class=cond-mat.mtrl-sci}} {{chem2|AlH5}},{{cite journal|last1=Hou|first1=Pugeng|last2=Zhao|first2=Xiusong|last3=Tian|first3=Fubo|last4=Li|first4=Da|last5=Duan|first5=Defang|last6=Zhao|first6=Zhonglong|last7=Chu|first7=Binhua|last8=Liu|first8=Bingbing|last9=Cui|first9=Tian|title=High pressure structures and superconductivity of AlH3(H2) predicted by first principles|journal=RSC Adv.|date=2015|volume=5|issue=7|pages=5096–5101|doi=10.1039/C4RA14990D|bibcode=2015RSCAd...5.5096H|s2cid=97440127}} {{chem2|GaH5}}, {{chem2|InH5}}, {{chem2|SnH8}}, {{chem2|SnH12}}, {{chem2|SnH14}},{{cite journal|last1=Mahdi Davari Esfahani|first1=M.|last2=Wang|first2=Zhenhai|last3=Oganov|first3=Artem R.|last4=Dong|first4=Huafeng|last5=Zhu|first5=Qiang|last6=Wang|first6=Shengnan|last7=Rakitin|first7=Maksim S.|last8=Zhou|first8=Xiang-Feng|title=Superconductivity of novel tin hydrides (Snn Hm) under pressure|journal=Scientific Reports|date=11 March 2016|volume=6|issue=1|pages=22873|doi=10.1038/srep22873|pmid=26964636|pmc=4786816|bibcode=2016NatSR...622873M|arxiv=1512.07604}} {{chem2|PbH8}},{{cite journal|last1=Cheng|first1=Ya|last2=Zhang|first2=Chao|last3=Wang|first3=Tingting|last4=Zhong|first4=Guohua|last5=Yang|first5=Chunlei|last6=Chen|first6=Xiao-Jia|last7=Lin|first7=Hai-Qing|date=12 November 2015|title=Pressure-induced superconductivity in H2-containing hydride PbH4(H2)2|journal=Scientific Reports|volume=5|issue=1|pages=16475|bibcode=2015NatSR...516475C|doi=10.1038/srep16475|pmid=26559369|pmc=4642309}} {{chem2|SiH8}} (subsequently discovered), {{chem2|GeH8}},{{cite journal|last1=Szcze¸śniak|first1=R.|last2=Szcze¸śniak|first2=D.|last3=Durajski|first3=A.P.|date=April 2014|title=Thermodynamics of the superconducting phase in compressed GeH4(H2)2|journal=Solid State Communications|volume=184|pages=6–11|bibcode=2014SSCom.184....6S|doi=10.1016/j.ssc.2013.12.036}} (although {{chem2|Ge3H11}} may be stable instead){{cite journal|last1=Davari Esfahani|first1=M. Mahdi|last2=Oganov|first2=Artem R.|last3=Niu|first3=Haiyang|last4=Zhang|first4=Jin|date=10 April 2017|title=Superconductivity and unexpected chemistry of germanium hydrides under pressure|journal=Physical Review B|volume=95|issue=13|pages=134506|bibcode=2017PhRvB..95m4506D|doi=10.1103/PhysRevB.95.134506|arxiv=1701.05600|s2cid=43481894}} {{chem2|AsH8}}, {{chem2|SbH4}},{{cite journal|last1=Fu|first1=Yuhao|last2=Du|first2=Xiangpo|last3=Zhang|first3=Lijun|last4=Peng|first4=Feng|last5=Zhang|first5=Miao|last6=Pickard|first6=Chris J.|last7=Needs|first7=Richard J.|last8=Singh|first8=David J.|last9=Zheng|first9=Weitao|date=22 March 2016|title=High-Pressure Phase Stability and Superconductivity of Pnictogen Hydrides and Chemical Trends for Compressed Hydrides|journal=Chemistry of Materials|volume=28|issue=6|pages=1746–1755|arxiv=1510.04415|doi=10.1021/acs.chemmater.5b04638|last10=Ma|first10=Yanming|s2cid=54571045}} {{chem2|BiH4}}, {{chem2|BiH5}}, {{chem2|BiH6}},{{cite arXiv|last1=Ma|first1=Yanbin|last2=Duan|first2=Defang|last3=Li|first3=Da|last4=Liu|first4=Yunxian|last5=Tian|first5=Fubo|last6=Yu|first6=Hongyu|last7=Xu|first7=Chunhong|last8=Shao|first8=Ziji|last9=Liu|first9=Bingbing|date=17 November 2015|title=High-pressure structures and superconductivity of bismuth hydrides|eprint=1511.05291|last10=Cui|first10=Tian|class=cond-mat.supr-con}} {{chem2|H3Se}},{{cite journal|last1=Zhang|first1=Shoutao|last2=Wang|first2=Yanchao|last3=Zhang|first3=Jurong|last4=Liu|first4=Hanyu|last5=Zhong|first5=Xin|last6=Song|first6=Hai-Feng|last7=Yang|first7=Guochun|last8=Zhang|first8=Lijun|last9=Ma|first9=Yanming|date=22 October 2015|title=Phase Diagram and High-Temperature Superconductivity of Compressed Selenium Hydrides|journal=Scientific Reports|volume=5|issue=1|pages=15433|bibcode=2015NatSR...515433Z|doi=10.1038/srep15433|pmid=26490223|pmc=4614537|arxiv=1502.02607}} {{chem2|H3S}},{{cite journal|last1=Durajski|first1=Artur P.|last2=Szczęśniak|first2=Radosław|date=30 June 2017|title=First-principles study of superconducting hydrogen sulfide at pressure up to 500 GPa|journal=Scientific Reports|volume=7|issue=1|pages=4473|bibcode=2017NatSR...7.4473D|doi=10.1038/s41598-017-04714-5|pmid=28667259|pmc=5493702}} {{chem2|Te2H5}}, {{chem2|TeH4}},{{cite journal|last1=Zhong|first1=Xin|last2=Wang|first2=Hui|last3=Zhang|first3=Jurong|last4=Liu|first4=Hanyu|last5=Zhang|first5=Shoutao|last6=Song|first6=Hai-Feng|last7=Yang|first7=Guochun|last8=Zhang|first8=Lijun|last9=Ma|first9=Yanming|date=4 February 2016|title=Tellurium Hydrides at High Pressures: High-Temperature Superconductors|journal=Physical Review Letters|volume=116|issue=5|pages=057002|bibcode=2016PhRvL.116e7002Z|doi=10.1103/PhysRevLett.116.057002|pmid=26894729|arxiv=1503.00396|s2cid=14435357}} {{chem2|PoH4}}, {{chem2|PoH6}}, {{chem2|H2F}}, {{chem2|H3F}}, {{chem2|H2Cl}}, {{chem2|H3Cl}}, {{chem2|H5Cl}}, {{chem2|H7Cl}},{{cite journal|last1=Duan|first1=Defang|last2=Huang|first2=Xiaoli|last3=Tian|first3=Fubo|last4=Liu|first4=Yunxian|last5=Li|first5=Da|last6=Yu|first6=Hongyu|last7=Liu|first7=Bingbing|last8=Tian|first8=Wenjing|last9=Cui|first9=Tian|title=Predicted Formation of H3+ in Solid Halogen Polyhydrides at High Pressures|journal=The Journal of Physical Chemistry A|date=12 November 2015|volume=119|issue=45|pages=11059–11065|doi=10.1021/acs.jpca.5b08183|pmid=26469181|bibcode=2015JPCA..11911059D}} {{chem2|H2Br}}, {{chem2|H3Br}}, {{chem2|H4Br}}, {{chem2|H5Br}}, {{chem2|H5I}}, {{chem2|XeH2}}, {{chem2|XeH4}}.{{cite journal|last1=Yan|first1=Xiaozhen|last2=Chen|first2=Yangmei|last3=Kuang|first3=Xiaoyu|last4=Xiang|first4=Shikai|title=Structure, stability, and superconductivity of new Xe–H compounds under high pressure|journal=The Journal of Chemical Physics|date=28 September 2015|volume=143|issue=12|pages=124310|doi=10.1063/1.4931931|pmid=26429014|bibcode=2015JChPh.143l4310Y|doi-access=free}}
Among the transition elements, {{chem2|VH8}} in a C2/m structure around 200 GPa is predicted to have a superconducting transition temperature of 71.4 K. {{chem2|VH5}} in a P63/mmm space group has a lower transition temperature.{{cite journal|last1=Li|first1=Xiaofeng|last2=Peng|first2=Feng|title=Superconductivity of Pressure-Stabilized Vanadium Hydrides|journal=Inorganic Chemistry|volume=56|issue=22|pages=13759–13765|date=2 November 2017|doi=10.1021/acs.inorgchem.7b01686|pmid=29094931}}
Properties
=Superconduction=
Under suitably high pressures polyhydrides may become superconducting. Characteristics of substances that are predicted to have high superconducting temperatures are a high phonon frequency, which will happen for light elements, and strong bonds. Hydrogen is the lightest and so will have the highest frequency of vibration. Even changing the isotope to deuterium will lower the frequency and lower the transition temperature. Compounds with more hydrogen will resemble the predicted metallic hydrogen. However, superconductors also tend to be substances with high symmetry and also need the electrons not to be locked into molecular subunits, and require large numbers of electrons in states near the Fermi level. There should also be electron-phonon coupling which happens when the electric properties are tied to the mechanical position of the hydrogen atoms.{{cite journal|last1=Peng|first1=Feng|last2=Sun|first2=Ying|last3=Pickard|first3=Chris J.|last4=Needs|first4=Richard J.|last5=Wu|first5=Qiang|last6=Ma|first6=Yanming|title=Hydrogen Clathrate Structures in Rare Earth Hydrides at High Pressures: Possible Route to Room-Temperature Superconductivity|journal=Physical Review Letters|date=8 September 2017|volume=119|issue=10|pages=107001|doi=10.1103/PhysRevLett.119.107001|pmid=28949166|url=https://www.repository.cam.ac.uk/bitstream/handle/1810/267416/RE-H%20compound.pdf?sequence=1|bibcode=2017PhRvL.119j7001P}}{{cite journal|last1=Pietronero|first1=Luciano|last2=Boeri|first2=Lilia|last3=Cappelluti|first3=Emmanuele|last4=Ortenzi|first4=Luciano|title=Conventional/unconventional superconductivity in high-pressure hydrides and beyond: insights from theory and perspectives|journal=Quantum Studies: Mathematics and Foundations|volume=5|pages=5–21|date=9 September 2017|doi=10.1007/s40509-017-0128-8|hdl=11573/1622515 |s2cid=139800480|hdl-access=free}}{{cite journal |last1=Pinsook |first1=Udomsilp |title=In search for near-room-temperature superconducting critical temperature of metal superhydrides under high pressure: A review |journal=Journal of Metals, Materials and Minerals |date=July 2020 |volume=30 |page=31 |doi=10.14456/jmmm.2020.18 |url=http://jmmm.material.chula.ac.th/index.php/jmmm/article/view/858}} The highest superconduction critical temperatures are predicted to be in groups 3 and 3 of the periodic table. Late transitions elements, heavy lanthanides or actinides have extra d- or f-electrons that interfere with superconductivity.{{cite journal |last1=Semenok |first1=Dmitrii V. |last2=Kruglov |first2=Ivan A. |last3=Savkin |first3=Igor A. |last4=Kvashnin |first4=Alexander G. |last5=Oganov |first5=Artem R. |title=On Distribution of Superconductivity in Metal Hydrides |journal=Current Opinion in Solid State and Materials Science |date=April 2020 |pages=100808 |doi=10.1016/j.cossms.2020.100808 |volume=24|issue=2 |arxiv=1806.00865 |bibcode=2020COSSM..24j0808S |s2cid=119433896}}
For example, lithium hexahydride is predicted to lose all electrical resistance below 38 K at a pressure of 150 GPa. The hypothetical {{chem2|LiH8}} has a predicted superconducting transition temperature at 31 K at 200 GPa.{{cite journal|last1=Xie|first1=Yu|last2=Li|first2=Quan|last3=Oganov|first3=Artem R.|last4=Wang|first4=Hui|title=Superconductivity of lithium-doped hydrogen under high pressure|journal=Acta Crystallographica Section C|date=31 January 2014|volume=70|issue=2|pages=104–111|doi=10.1107/S2053229613028337|pmid=24508954}} {{chem2|MgH6}} is predicted to have a Tc of 400 K around 300 GPa.{{cite journal|last1=Szczȩśniak|first1=R.|last2=Durajski|first2=A. P.|title=Superconductivity well above room temperature in compressed MgH6|journal=Frontiers of Physics|date=13 July 2016|volume=11|issue=6|pages=117406|doi=10.1007/s11467-016-0578-1|bibcode=2016FrPhy..11k7406S|s2cid=124245616}} {{chem2|CaH6}} could have a Tc of 260 K at 120 GPa. {{chem2|PH3}} doped {{chem2|H3S}} is also predicted to have a transition temperature above the 203 K measured for {{chem2|H3S}} (contaminated with solid sulfur).{{cite journal|last1=Eremets|first1=M I|last2=Drozdov|first2=A P|title=High-temperature conventional superconductivity|journal=Physics-Uspekhi|date=30 November 2016|volume=59|issue=11|pages=1154–1160|doi=10.3367/UFNe.2016.09.037921|bibcode=2016PhyU...59.1154E|s2cid=126290095}} Rare earth and actinide polyhydrides may also have highish transition temperatures, for example, {{chem2|ThH10}} with Tc = 241 K. {{chem2|UH8}}, which can be decompressed to room temperature without decomposition, is predicted to have a transition temperature of 193 K. {{chem2|AcH10}}, if it could be ever made, is predicted to superconduct at temperatures over 204 K, and {{chem2|AcH10}} would be similarly conducting under lower pressures (150 GPa).{{cite journal|arxiv=1802.05676|last1=Semenok|first1=Dmitrii V|title=Actinium hydrides AcH10, AcH12, AcH16 as high-temperature conventional superconductors|journal=The Journal of Physical Chemistry Letters|volume=9|issue=8|pages=1920–1926|last2=Kvashnin|first2=Alexander G|last3=Kruglov|first3=Ivan A|last4=Oganov|first4=Artem R|year=2018|doi=10.1021/acs.jpclett.8b00615|pmid=29589444|s2cid=4620593}}
{{chem2|H3Se}} actually is a van der Waals solid with formula {{chem2|2H2Se*H2}} with a measured Tc of 105 K under a pressure of 135 GPa.
=Ternary superhydrides=
Ternary superhydrides open up the possibility of many more formulas.{{cite journal |last1=Sukmas |first1=Wiwittawin |last2=Tsuppayakorn-aek |first2=Prutthipong |last3=Pinsook |first3=Udomsilp |last4=Bovornratanaraks |first4=Thiti |title=Near-room-temperature superconductivity of Mg/Ca substituted metal hexahydride under pressure |journal=Journal of Alloys and Compounds |date=30 December 2020 |volume=849 |page=156434 |doi=10.1016/j.jallcom.2020.156434 |s2cid=225031775 |url=https://www.sciencedirect.com/science/article/abs/pii/S0925838820327985|url-access=subscription }} For example, {{chem2|Li2MgH16}} may also be superconducting at high temperatures (200 °C).{{cite journal |last1=Flores-Livas |first1=José A. |last2=Arita |first2=Ryotaro |title=A Prediction for "Hot" Superconductivity |journal=Physics |date=26 August 2019 |volume=12 |page=96 |doi=10.1103/Physics.12.96|bibcode=2019PhyOJ..12...96F |doi-access=free}} A compound of lanthanum, boron and hydrogen is speculated to be a "hot" superconductor (550 K).{{cite journal |last1=Grockowiak |first1=A. D. |last2=Ahart |first2=M. |last3=Helm |first3=T. |last4=Coniglio |first4=W. A. |last5=Kumar |first5=R. |last6=Somayazulu |first6=M. |last7=Meng |first7=Y. |last8=Oliff |first8=M. |last9=Williams |first9=V. |last10=Ashcroft |first10=N. W. |last11=Hemley |first11=R. J. |last12=Tozer |first12=S. W. |title=Hot Hydride Superconductivity Above 550 K |journal=Frontiers in Electronic Materials |year=2022 |volume=2 |doi=10.3389/femat.2022.837651 |arxiv=2006.03004 |language=en|doi-access=free}}{{cite arXiv |last1=Di Cataldo |first1=Simone |last2=von der Linden |first2=Wolfgang |last3=Boeri |first3=Lilia |title=La-$X$-H hydrides: is hot superconductivity possible? |date=2021-06-14 |class=cond-mat.supr-con |eprint=2106.07266}} Elements may substitute for others and so modify the properties eg {{chem2|(La,Y)H6}} and {{chem2|(La,Y)H10}} can be made to have a slightly higher critical temperature than {{chem2|YH6}} or {{chem2|LaH10}}.{{cite journal |last1=Semenok |first1=Dmitrii V. |last2=Troyan |first2=Ivan A. |last3=Ivanova |first3=Anna G. |last4=Kvashnin |first4=Alexander G. |last5=Kruglov |first5=Ivan A. |last6=Hanfland |first6=Michael |last7=Sadakov |first7=Andrey V. |last8=Sobolevskiy |first8=Oleg A. |last9=Pervakov |first9=Kirill S. |last10=Lyubutin |first10=Igor S. |last11=Glazyrin |first11=Konstantin V. |last12=Giordano |first12=Nico |last13=Karimov |first13=Denis N. |last14=Vasiliev |first14=Alexander L. |last15=Akashi |first15=Ryosuke |last16=Pudalov |first16=Vladimir M. |last17=Oganov |first17=Artem R. |title=Superconductivity at 253 K in lanthanum–yttrium ternary hydrides |journal=Materials Today |date=July 2021 |volume=48 |pages=18–28 |doi=10.1016/j.mattod.2021.03.025|arxiv=2012.04787 |s2cid=228064078}}
See also
- Potassium nonahydridorhenate, stable at ordinary pressures