X-ray study of niobium disulfide intercalated with copper

Abstract

Bondlengths of nearest neighbours around the Cu and Nb atoms in a Cuo.5NbS2 single crystal are extracted from the extended X-ray absorption fine structure (EXAFS) and lattice parameters are measured by X-ray diffraction. It is found that the Cu atoms occupy tetrahedral sites in the Van der Wads gap. Upon intercalation the NbS, sandwiches are squeezed by 0.009 nm whereas the van der Waals gap expands by 0.067 nm. The Nb-Nb distance in the NbS, layers increases by 0.003 nm. The Nb-S bond length shortens by 0.001 nm. The positions of the K-edge energies indicate a charge transfer from the Cu atoms to the host sandwich layers.Bindungslangen zu nachsten Nachbarn um die Cu-und Nb-Atome in einem Cuo,5NbS2-EinkristaIl werden aus der kantenfernen Rontgenabsorptionsfeinstruktur (EXAFS) ermittelt und die Gitt,erkonstanten werden mittels Rontgenbeugung gemessen. Es wird festgestellt, da13 die Cu-Atome Tetraederlucken in der Van-der-Waals-Liicke besetzen. Durch clie Interkalation werden die NbS,-Schichten um 0,009 nm ZusammengepreIJt,, wahrend sich die van-der-~~aa.ls-Licke urn 0,067 nm aufweitet. Der Nb-Nb-Absta.nd in den NbS,-Schichten wird nm 0,003 nm gro13er. Die Nb-S Bindungslange wird um 0,001 nm lriirzer. Die energetischen Lagen der K-Kanten weisen auf einen Ladungst.ransfer von den Cu-Atomen zu den Schichten des Wirtskrist,alls hin.

Spontaneous self-intercalation of copper atoms into transition metal dichalcogenides

“…It revealed that some of Cu atoms were peeled off the surface of 2H-NbS 2 at this high temperature, until the atomic ratio drops to 0.6:1.0 (Cu:Nb). This theoretical maximum intercalant concentration is close to a previous experimental value obtained in high-temperature synthesis (18,19). Fig.…”

“…S17), suggesting that a saturation of Cu intercalation state would be reached at this point. The homogeneous Cu 1.2 NbS 2 has a much higher intercalation state than the previous ones synthesized at high temperatures (16)(17)(18)(19)(20)(21). Our experimental saturation of Cu intercalation state is very close to that from the DFT calculations (table S1).…”

“…S18). Accordingly, the neighboring Nb-Nb distance along the c axis (d Nb-Nb = c/2) increases from 0.597 nm for 2H-NbS 2 to 0.661 nm for Cu 1.2 NbS 2 , owing mainly to the expanding of interlayer spacing upon Cu intercalation since the sandwiched NbS 2 slab height only changes slightly (19,34). The swelling of d Nb-Nb leads to the gradual shift of (002) peak of Cu x NbS 2 to a lower diffraction angle until x = 1.2 upon which the diffraction peaks of Cu completely disappears ( fig.…”

“…A large number of transition metal atoms could intercalate into group IV and V layered TMDs to form well-defined intercalation compounds, M′ x MX 2 (M′ is the intercalation metal different from the one in the host material, x intercalation state) (14,15). Most of them were synthesized by the solid-state reaction or chemical iodine-vapor transport (CVT) methods, both at the elevated temperatures (650° to 1100°C) (16)(17)(18)(19)(20)(21). This high-temperature solid or vapor phase reaction forms homogeneous intercalation compounds; however, some defects are introduced into TMDs hosts, and meanwhile, the process is energy and time intensive.…”

Crystal structure and staging of CuxNbSe2 and AgxNbSe2

“…It will be recalled that the model used to interpret the current X-ray results assumes the copper is equally divided over the available sites which is completely consistent with the results just stated [la]. I n addition to the evidence already cited that the Cu enters tetrahedral sites [4, 51 in Cu,NbSe,, it should be noted that EXAFS and X-ray diffraction on the analogous material Cuo,6NbS, show that Cu enters the tetrahedral sites in NbS, [13].…”