Novel High-Pressure Yttrium Carbide γ−Y4C5 Containing [

Alena Aslandukovа

¹

,

Andrey Aslandukov

²

,

Liang Yuan

³

et al.

Abstract

Changes in the bonding of carbon under high pressure leads to unusual crystal chemistry and can dramatically alter the properties of transition metal carbides. In this work, the new orthorhombic polymorph of yttrium carbide, γ-Y 4 C 5 , was synthesized from yttrium and paraffin oil in a laser-heated diamond anvil cell at ∼50 GPa. The structure of γ-Y 4 C 5 was solved and refined using in situ synchrotron single-crystal x-ray diffraction. It includes two carbon groups: [C 2 ] dimers and nonlinear [C 3 ] trimers. Crystal chemical analysis and density functional theory calculations revealed unusually high noninteger charges (½C 2 5.2− and ½C 3 6.8− ) and unique bond orders (<1.5). Our results extend the list of possible carbon states at extreme conditions.

High-pressure hP3 yttrium allotrope with CaHg2 -type structure as a prototype of the hP3

“…The reason is that there are still many open questions regarding, for example, the origin of the superconducting effect and the structure (or chemical composition) of the materials for which the phenomenon is described [10][11][12]. Some problems with the currently available experimental data interpretation may be associated with the synthesis technique: hydrides at HP are often obtained by heating metals embedded in paraffin oil or ammonia borane [3,[6][7][8][13][14][15], and one cannot exclude that other nonhydride phases (e.g., car-* alena.aslandukova@uni-bayreuth.de bon and boron compounds) may form in the system under 48 investigation [16,17], and their properties can influence the 49 measurements of superconductivity.…”

High-pressure synthesis of dysprosium carbides

“…For 19 simple binary metal-nitrogen compounds containing [N 2 ] x – species, a linear correlation was found between the length of the N–N dimers and their formal charges ( Laniel et al, 2022 ). We used the literature data on 12 metal carbides studied at ambient conditions ( Atoji et al, 1958 ; Spedding et al, 1958 ; Atoji, 1967b ; 1967a ; Krupka et al, 1969 ; Adachi et al, 1976 ; Czekalla et al, 1997 ; Vohn et al, 2000 ; 1999 ; Yosida, 2002 ; Babizhetskyy et al, 2014 ; Aslandukova et al, 2021 ) and our own results to analyse the relationship between the length of carbon dimers and their formal charges. For the novel Dy 3 C 2 , the C-C length at ambient pressure was obtained by DFT calculations, as well as for γ-Y 4 C 5 in ( Aslandukova et al, 2021 ); for Dy 2 C 3 we included both the experimental value ( Spedding et al, 1958 ) and the one DFT-calculated in this work, as they are a bit different.…”

“…All data corresponds to ambient pressure. Literature data are from experiments [( Atoji et al, 1958 ; Spedding et al, 1958 ; Atoji, 1967b ; 1967a ; Krupka et al, 1969 ; Adachi et al, 1976 ; Czekalla et al, 1997 ; Vohn et al, 2000 ; 1999 ; Yosida, 2002 ; Babizhetskyy et al, 2014 ; Aslandukova et al, 2021 )], except for γ-Y 4 C 5 ( Aslandukova et al, 2021 ) and for Dy 2 C 3 and Dy 3 C 2 (this work, DFT-computed structures fully relaxed at 1 bar).…”

“…We used the literature data on 12 metal carbides studied at ambient conditions (Atoji et al, 1958;Spedding et al, 1958;Atoji, 1967b;1967a;Krupka et al, 1969;Adachi et al, 1976;Czekalla et al, 1997;Vohn et al, 2000;Yosida, 2002;Babizhetskyy et al, 2014;Aslandukova et al, 2021) and our own results to analyse the relationship between the length of carbon dimers and their formal charges. For the novel Dy 3 C 2 , the C-C length at ambient pressure was obtained by DFT calculations, as well as for γ-Y 4 C 5 in (Aslandukova et al, 2021); for Dy 2 C 3 we included both the experimental value (Spedding et al, 1958) and the one DFTcalculated in this work, as they are a bit different. It appeared that the linear correlation holds also for carbides featuring [C 2 ] x− dimers at ambient conditions (Figure 4).…”

“…Considering that vast amount of the data corresponds to ambient conditions, the chemistry of carbides under high pressure has been poorly studied in principle. A recent discovery ( Aslandukova et al, 2021 ) of the new γ-Y 4 C 5 phase with non-linear [C 3 ] groups synthesized above 40 GPa illustrates the importance of investigations of carbides at high pressures and motivates further studies of lanthanides carbides at non-ambient conditions. In this work, we report the high-pressure synthesis in laser-heated diamond anvil cells (DACs) of two novel carbides Dy 4 C 3 and Dy 3 C 2 , and the formation of dysprosium sesquicarbide Dy 2 C 3 , already known at ambient conditions.…”