High-pressure synthesis of dysprosium carbides

Chemical reactions between dysprosium and carbon were studied in laser-heated diamond anvil cells at pressures of 19, 55, and 58 GPa and temperatures of ∼2500 K. In situ single-crystal synchrotron X-ray diffraction analysis of the reaction products revealed the formation of novel dysprosium carbides, Dy4C3 and Dy3C2, and dysprosium sesquicarbide Dy2C3 previously known only at ambient conditions. The structure of Dy4C3 was found to be closely related to that of dysprosium sesquicarbide Dy2C3 with the Pu2C3-type structure. Ab initio calculations reproduce well crystal structures of all synthesized phases and predict their compressional behavior in agreement with our experimental data. Our work gives evidence that high-pressure synthesis conditions enrich the chemistry of rare earth metal carbides

Polytypism of Incommensurately Modulated Structures of Crystalline Bromine upon Molecular Dissociation under High Pressure

Polytypism of incommensurately modulated structures was hitherto unobserved. Here, we found the phenomenon in simple halogen systems of bromine and iodine upon molecular dissociation in the solids under pressure. Single-crystal synchrotron X-ray diffraction in laser heated diamond anvil cells pressurised up to 112 GPa revealed a number of allotropes of bromine and iodine including polytypes of Br-III{\gamma} (Fmmm(00{\gamma})s00) with {\gamma} varying within 0.18 to 0.3

High-pressure synthesis of dysprosium carbides

Chemical reactions between dysprosium and carbon were studied in laser-heated diamond anvil cells at pressures of 19, 55, and 58 GPa and temperatures of ∼2500 K. In situ single-crystal synchrotron X-ray diffraction analysis of the reaction products revealed the formation of novel dysprosium carbides, Dy$_4$C$_3$ and Dy$_3$C$_2$, and dysprosium sesquicarbide Dy$_2$C$_3$ previously known only at ambient conditions. The structure of Dy$_4$C$_3$ was found to be closely related to that of dysprosium sesquicarbide Dy$_2$C$_3$ with the Pu$_2$C$_3$-type structure. Ab initio calculations reproduce well crystal structures of all synthesized phases and predict their compressional behavior in agreement with our experimental data. Our work gives evidence that high-pressure synthesis conditions enrich the chemistry of rare earth metal carbides

High-pressure hP3hP3 yttrium allotrope with CaHg2_2 -type structure as a prototype of the hP3hP3 rare-earth hydride series

A novel high-pressure yttrium allotrope, $hP3$-Y (space group $P6/mmm$), was synthesized in a multi-anvil press at 20 GPa and 2000 K which is recoverable to ambient conditions. Its relative stability and electronic properties were investigated using density functional theory calculations. A $hP3$-Y derivative hydride, $hP3-YHx$, with a variable hydrogen content ($x = 2.8$, 3, 2.4), was synthesized in diamond anvil cells by the direct reaction of yttrium with paraffin oil, hydrogen gas, and ammonia borane upon laser heating to ~3000 K at 51, 45 and 38 GPa, respectively. Room-temperature decompression leads to gradual reduction and eventually the complete loss of hydrogen at ambient conditions. Isostructural $hP3-NdHx$ and $hP3-GdHx$ hydrides were synthesized from Nd and Gd metals and paraffin oil, suggesting that the $hP3$-Y structure type may be common for rare-earth elements. Our results expand the list of allotropes of trivalent lanthanides and their hydrides and suggest that they should be considered in the context of studies of high-pressure behavior and properties of this broad class of materials

Diverse high-pressure chemistry in Y-NH₃BH₃ and Y–paraffin oil systems

The yttrium-hydrogen system has gained attention because of near-ambient temperature superconductivity reports in yttrium hydrides at high pressures. We conducted a study using synchrotron single-crystal x-ray diffraction (SCXRD) at 87 to 171 GPa, resulting in the discovery of known (two YH3 phases) and five previously unknown yttrium hydrides. These were synthesized in diamond anvil cells by laser heating yttrium with hydrogen-rich precursors—ammonia borane or paraffin oil. The arrangements of yttrium atoms in the crystal structures of new phases were determined on the basis of SCXRD, and the hydrogen content estimations based on empirical relations and ab initio calculations revealed the following compounds: Y3H11, Y2H9, Y4H23, Y13H75, and Y4H25. The study also uncovered a carbide (YC2) and two yttrium allotropes. Complex phase diversity, variable hydrogen content in yttrium hydrides, and their metallic nature, as revealed by ab initio calculations, underline the challenges in identifying superconducting phases and understanding electronic transitions in high-pressure synthesized materials

Stabilization Of The CN3_35−^{5−} Anion In Recoverable High‐pressure Ln3_3O2_2(CN3_3) (Ln=La, Eu, Gd, Tb, Ho, Yb) Oxoguanidinates

A series of isostructural Ln$_3$O$_2$(CN$_3$) (Ln=La, Eu, Gd, Tb, Ho, Yb) oxoguanidinates was synthesized under high-pressure (25–54 GPa) high-temperature (2000–3000 K) conditions in laser-heated diamond anvil cells. The crystal structure of this novel class of compounds was determined via synchrotron single-crystal X-ray diffraction (SCXRD) as well as corroborated by X-ray absorption near edge structure (XANES) measurements and density functional theory (DFT) calculations. The Ln$_3$O$_2$(CN$_3$) solids are composed of the hitherto unknown CN$_3$$^{5−}$ guanidinate anion—deprotonated guanidine. Changes in unit cell volumes and compressibility of Ln$_3$O$_2$(CN$_3$) (Ln=La, Eu, Gd, Tb, Ho, Yb) compounds are found to be dictated by the lanthanide contraction phenomenon. Decompression experiments show that Ln$_3$O$_2$(CN$_3$) compounds are recoverable to ambient conditions. The stabilization of the CN$_3$$^{5−}$ guanidinate anion at ambient conditions provides new opportunities in inorganic and organic synthetic chemistry

Unraveling the Bonding Complexity of Polyhalogen Anions: High-Pressure Synthesis of Unpredicted Sodium Chlorides Na2_2Cl3_3 and Na4_4Cl5_5 and Bromide Na4_4Br5_5

The field of polyhalogen chemistry, specifically polyhalogen anions (polyhalides), is rapidly evolving. Here, we present the synthesis of three sodium halides with unpredicted chemical compositions and structures (tP10-Na$_2$Cl$_3$, hP18-Na$_4$Cl$_5$, and hP18-Na$_4$Br$_5$), a series of isostructural cubic cP8-AX$_3$ halides (NaCl$_3$, KCl$_3$, NaBr$_3$, and KBr$_3$), and a trigonal potassium chloride (hP24-KCl$_3$). The high-pressure syntheses were realized at 41–80 GPa in diamond anvil cells laser-heated at about 2000 K. Single-crystal synchrotron X-ray diffraction (XRD) provided the first accurate structural data for the symmetric trichloride Cl3– anion in hP24-KCl3 and revealed the existence of two different types of infinite linear polyhalogen chains, [Cl]$_∞$$^{n–}$ and [Br]$_∞$$^{n–}$, in the structures of cP8-AX$_3$ compounds and in hP18-Na$_4$Cl$_5$ and hP18-Na$_4$Br$_5$. In Na$_4$Cl$_5$ and Na$_4$Br$_5$, we found unusually short, likely pressure-stabilized, contacts between sodium cations. Ab initio calculations support the analysis of structures, bonding, and properties of the studied halogenides