Plutonium sulfides are compounds of plutonium and sulfur, where sulfur exists as sulfide or polysulfide ions and plutonium exists in the trivalent state or tetravalent state. They have a general formula PuxSy. Known plutonium sulfides include PuS, Pu3S4, Pu5S7, Pu2S3, and PuS2. Plutonium oxysulfides (mixed oxide-sulfides) are also known, including Pu2O2S, Pu4O4S3, PuOS, and Pu2O2S3. Many of them are isostructural to the corresponding neptunium sulfides.[1][2]
Plutonium monosulfide is a yellow solid with the formula PuS. Unlike neptunium and uranium monosulfide, it contains plutonium in its tetravalent state, rather than trivalent.[3] It is produced in several chemical reactions:[2][4]
It is formed during the reaction of plutonium metal and sulfur gas:[4]
Pu + S → PuS
It is also formed when plutonium sesquisulfide is reduced by plutonium hydride.[2]
Reacting ground plutonium metal with hydrogen sulfide also produces plutonium monosulfide.[2]
It is a non-stoichiometric compound, having a range between around PuS0.95 and PuS1.00. At Pu:S ratios lower than 0.95 or higher than 1.00, it exists in equilibrium with plutonium metal or plutonium sesquisulfide, respectively.[2]
At room temperature and pressure, it adopts the rock salt structure. Its structure is cubic, with space groupFm3m and lattice parameter a=5.23–5.24 Å depending on stoichiometry; its lattice parameter decreases with decreasing sulfur content. It does not exhibit a phase transition up to 60 GPa, but theoretical predictions it should undergo a phase transition to a caesium chloride-type structure at 105 GPa, undergoing a 3.6% volume loss.[3]
Plutonium sesquisulfide
Structure of α-Pu2S3.
Plutonium sesquisulfide has the formula Pu2S3. It can be formed from the reaction between plutonium metal and sulfur gas:[4]
2 Pu + 3 S → Pu2S3
Or from the thermal decomposition of plutonium disulfide:[4]
2 PuS2 → Pu2S3 + S
Three polymorphs of plutonium sesquisulfide are known: α-Pu2S3, β-Pu2S3 and γ-Pu2S3, though β-Pu2S3 is a ternary oxysulfide and can feature incorporated oxygen.[2][4][5]
Like with the neptunium sulfides, α-Pu2S3 is a stoichiometric compound, while β-Pu2S3 and γ-Pu2S3 have variable composition. β-Pu2S3 is a solid solution between Pu10S14O and Pu2S3 (formula Pu10S15-xOx) and γ-Pu2S3 is substoichiometric with an ideal composition of Pu3S4.[1][2][5]
α-Pu2S3 is the dominant form of Pu2S3 up to 1100 °C. At 1100 °C, it decomposes to the β-Pu2S3, and at 1550 °C, β-Pu2S3 decomposes to γ-Pu2S3.[2]γ-Pu2S3 melts above 1700 °C; however, its melting point is dependent on its stoichiometry. Pu2S3 melts around 1725 °C, but Pu3S4 melts around 1820 °C.[2]
Structural properties
α-Pu2S3 has the same structure as the related rare earth compounds, having the La2S3-type structure, isostructural with α-Np2S3 and α-Ce2S3. It features a framework of PuS7 and PuS8 polyhedra. Its crystals are orthorhombic, with lattice parameters a=3.97, b=7.37, and c=15.45 Å. It has a density of 8.31 g/cm3 and space groupPnma.[2][4]
While early reports suggested β-Pu2S3 was a binary substoichiometric sulfide,[2] it was later shown[6] that the rare earth sesquisulfide phases, including β-Pu2S3, actually contain variable amounts of oxygen as opposed to sulfur vacancies, and it is now known to have variable composition between Pu2S3 and Pu10S14O, with a single site where oxygen and sulfur substitute for each other. It adopts a complex tetragonal structure of space group I41/acd which notably contains a Pu4O tetrahedron.[4][6][5] One crystal of this compound was found to have lattice parameters a=14.90, b=19.78 Å.[2]
γ-Pu2S3 adopts a Th3P4-type structure of space group I43d and bcc symmetry, where each plutonium atoms is coordinated to 8 atoms of sulfur. It extends over a large range of stoichiometries, from Pu3S4 to Pu2S3. Its lattice parameter is dependent on its stoichiometry; Pu3S4 has lattice parameter around a=8.415 Å, while Pu2S3 has lattice parameter a=8.453–8.459 Å, though this depends on the exact conditions.[2][4]
Plutonium disulfide
Plutonium disulfide has the formula PuS2. It is the highest sulfide of plutonium. It is formed by the reaction of plutonium hydride and sulfur in a sealed tube for one week at about 350 °C to 750 °C, or by reacting plutonium and sulfur vapor together:[4]
Pu + 2S → PuS2
It adopts an anti-Fe2As type structure, with distortions that arise from disulfide bonding between sulfur atoms. It is often substoichiometric, and its composition range extends from PuS2.0 to around PuS1.76. Its structure can be either tetragonal (space group P4/nmm) or monoclinic (space group P21/a), though the monoclinic phase can only be found at the exact composition PuS2. Its lattice parameters vary depending on sulfur content; PuS1.76 has lattice parameters a=3.936 and c=7.958 Å, PuS1.9 has lattice parameters a=3.943 and c=7.962 Å, and tetragonal PuS2.0 has lattice parameters a=3.974 and c=7.947 Å. The monoclinic PuS2.0 phase has lattice parameters a=7.962, b=3.981, c=7.962 Å, and β=90°.[4]
Plutonium disulfide is thermally unstable, and upon calcination, it decomposes to lower plutonium sulfides. PuS2 first loses sulfur at 500 °C to give PuS1.9, which further loses sulfur at 580 °C to give α-Pu2S3.[4][2]
1 2 3 Besançon, Pierre (1973). "Teneur en oxygéne et formule exacte d'une famille de composés habituellement appelés "variété β" ou "phase complexe" des sulfures de terres rares". Journal of Solid State Chemistry. 7 (2): 232–240. doi:10.1016/0022-4596(73)90159-X.
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
