Phase mixtures and staging in intercalated LixNbSe2

Dahn, Douglas C.; Haering, R. R.

doi:10.1016/0038-1098(82)90706-2

Cited by 54 publications

(18 citation statements)

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“…Dense and dilute stages as well as complex staging (i.e. stage superstructures with different intercalate densities in different layers) are frequently observed in intercalation compounds 17,18 and may account for the observed spacings. The relative proportions observed for the pristine, stage 1 and the stage 2 phases in the different samples were found to depend on the concentration of the naphthyl-sodium solution as well as on the ratio Na:HfNCl.…”

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confidence: 97%

A new intermediate intercalate in superconducting sodium-doped hafnium nitride chloride

et al. 2005

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A new phase has been observed during the sodium intercalation of hafnium nitride chloride as intermediate between the host b-HfNCl and the already reported Na 0.29 HfNCl with T c of 24 K; the new intermediate shows interlayer spacings ranging from 9.48 to 9.67 Å , corresponds to a second stage intercalate of HfNCl and is superconducting with a critical temperature of 20 K.Intercalated zirconium and hafnium nitride halides have been reported to exhibit superconductivity with high critical temperatures within non oxidic compounds. 1,2 The pristine compounds MNX (M 5 Zr, Hf; X 5 Cl, Br, I) show two layered polytypes, a and b phases, isotypic to FeOCl and SmSI respectively. 3,4-6 The structure of the b phase can be described as a stacking along the c axis of double layers with composition [X-M-N-N-M-X], separated by a van der Waals gap. Superconductivity in ZrNX or HfNX is induced by intercalation of alkaline metals or Lewis bases as cobaltocene or pyridine into the van der Waals gap. [1][2][3]5,7 For sodium intercalated hafnium nitride chloride a superconducting phase has been reported with critical temperatures of 20, 23 or 24 K 8-11 and in lithium intercalated HfNCl, critical temperatures of 18, 20, 24 and 26 K have been observed in different samples showing in some cases co-intercalated organic molecules. 2,12,13 In both systems as well as in doped zirconium nitride chloride that shows lower critical temperatures (close to 12 K), the influence on the critical temperature of factors such as the nature of the transition metal, the co-intercalated molecules and the doping level have still not been completely understood. The crystal structure of Na x HfNCl with x 5 0.29 has been reported as isotypic to YOF with space group R3m and crystal parameters a 5 3.5892(3) Å and c 5 29.722(3) Å . 8 The interlayer spacing is 1/3 of the c parameter, being 9.80 Å for Na 0.29 HfNCl and 9.22 Å for the pristine. 3 Staging during intercalation of layered compounds is a phenomenon that has been frequently observed in graphite and in transition metal dichalcogenides, in which a unit consisting of a guest layer followed by n host layers (for a stage-n compound) is repeated along the c axis. 14,15 The phase Na 0.29 HfNCl has been described as a diluted stage 1 intercalate, with all the van der Waals gaps partially filled with sodium atoms. Here we report a new intercalated phase, with interlayer spacing between 9.48 and 9.67 Å that is obtained as an intermediate in the intercalation process of the host to give Na 0.29 HfNCl. The new phase shows a critical temperature of 20 K and can be interpreted as a second stage intercalate of HfNCl.HfNCl or ZrNCl were prepared by reaction of hafnium (Aldrich 99.5%) or zirconium (Alfa 99.9%) and ammonium chloride (Aldrich 99.99%) in the stoichiometric ratio 1:1.1 at temperatures between 740 and 780 uC during 12 hours in sealed evacuated silica tubes. In a second step a temperature gradient of 100 uC was applied to the same reaction tube and HfNCl and ZrNCl were recrystallized by chemical vapour trans...

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A new intermediate intercalate in superconducting sodium-doped hafnium nitride chloride

et al. 2005

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“…The 6H phase is, to our knowledge, the first example of the odd staging other than the first staging in intercalated TMDs synthesized via a solid-state reaction. Other examples of odd staging formed upon intercalation have been obtained in intercalation via electrochemistry 43 (Li x NbSe 2 ) or hydration. 44 Moreover, both 6R and 6H phases represent new polymorphs in the NbSe 2 system.…”

Section: ■ Resultsmentioning

confidence: 99%

“…The energy associated with this demands a minimum alkali concentration and the presence of a two-phase region at low alkali concentration, often leading to the formation of multistage compounds . The structures with second and fourth staging have been commonly observed in the intercalated TMDs; however, the structures with odd staging except one staging only exist in the hydrated phase and the electrochemically intercalated sample such as Li x NbSe 2 . , The 6H phase of Rb-intercalated NbSe 2 stands out as the first third staging prepared by solid-state reaction for the intercalated TMDs, which enriches the structure of intercalated TMDs. To the best of our knowledge, this work represents the first appearance of 6R and 6H phases in metal-intercalated 2H-NbSe 2 via a solid-state reaction mechanism.…”

Section: Discussionmentioning

confidence: 99%

“…44 The structures with second and fourth staging have been commonly observed in the intercalated TMDs; however, the structures with odd staging except one staging only exist in the hydrated phase and the electrochemically intercalated sample such as Li x NbSe 2 . 43,44 The 6H phase of ≤ x ≤ 1). The intercalated Na and K atoms usually occupy either trigonal prismatic sites (e.g., Na 0.5 NbSe 2 30 and K 0.67 NbSe 2 ) or octahedral sites (e.g., NaNbSe 2 and KNbSe 2 ).…”

Section: ■ Discussionmentioning

confidence: 99%

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Effects of Rb Intercalation on NbSe₂: Phase Formation, Structure, and Physical Properties

et al. 2019

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Here, we report the crystal structures and properties of Rb x NbSe 2 , with 0 ≤ x ≤ 0.5. With Rb intercalation, Rb x NbSe 2 evolves from 2H (Phase I) for 0 ≤ x ≤ 0.025, to 6R (Phase II) for x ∼ 0.2 with space group R3m (no. 166), and finally to 2H (Phase IV) for 0.375 ≤ x ≤ 0.5 with space group P6 3 /mmc (no. 194). In addition, Phase II is found to transform to a rare 6H structure (Phase III) with space group P6 3 /mmc (no. 194) by annealing at a relatively low temperature. We show the first 6H phase in the intercalated transition-metal dichalcogenides (TMDs) family obtained through a solid-state reaction. Moreover, both 6R and 6H phases are new polymorphs in the NbSe 2 system. For the range 0.2 ≤ x ≤ 0.5 in Rb x NbSe 2 , we show metallic electronic transport behavior and a paramagnetic feature. The lack of superconductivity (SC) down to 2 K is most probably due to the decrease of hole carrier density with increasing Rb content. Through careful analysis of the structural data, we were able to assemble a phase diagram covering the range of 0 ≤ x ≤ 0.5 in Rb x NbSe 2 .

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“…This peak corresponds to the 003 reflection and its position yields thus a direct measure of the interlayer separation of the intercalated and pristine compounds. The resolution achieved in our X-ray diffraction patterns allows the conclusion that all the sodium intercalated samples are a mixture of either the pristine 17,18 and may account for the observed spacings. The relative proportions observed for the pristine, stage 1 and the stage 2 phases in the different samples were found to depend on the concentration of the naphthyl-sodium solution as well as on the ratio Na:HfNCl.…”

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A New Intermediate Intercalate in Superconducting Sodium‐Doped Hafnium Nitride Chloride.

Oró‐Solé¹,

Frontera²,

Martı́nez³

et al. 2005

ChemInform

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A new phase has been observed during the sodium intercalation of hafnium nitride chloride as intermediate between the host b-HfNCl and the already reported Na 0.29 HfNCl with T c of 24 K; the new intermediate shows interlayer spacings ranging from 9.48 to 9.67 Å , corresponds to a second stage intercalate of HfNCl and is superconducting with a critical temperature of 20 K.Intercalated zirconium and hafnium nitride halides have been reported to exhibit superconductivity with high critical temperatures within non oxidic compounds. In both systems as well as in doped zirconium nitride chloride that shows lower critical temperatures (close to 12 K), the influence on the critical temperature of factors such as the nature of the transition metal, the co-intercalated molecules and the doping level have still not been completely understood. The crystal structure of Na x HfNCl with x 5 0.29 has been reported as isotypic to YOF with space group R3m and crystal parameters a 5 3.5892(3) Å and c 5 29.722(3) Å . 8 The interlayer spacing is 1/3 of the c parameter, being 9.80 Å for Na 0.29 HfNCl and 9.22 Å for the pristine. Staging during intercalation of layered compounds is a phenomenon that has been frequently observed in graphite and in transition metal dichalcogenides, in which a unit consisting of a guest layer followed by n host layers (for a stage-n compound) is repeated along the c axis.14,15 The phase Na 0.29 HfNCl has been described as a diluted stage 1 intercalate, with all the van der Waals gaps partially filled with sodium atoms. Here we report a new intercalated phase, with interlayer spacing between 9.48 and 9.67 Å that is obtained as an intermediate in the intercalation process of the host to give Na 0.29 HfNCl. The new phase shows a critical temperature of 20 K and can be interpreted as a second stage intercalate of HfNCl.HfNCl or ZrNCl were prepared by reaction of hafnium (Aldrich 99.5%) or zirconium (Alfa 99.9%) and ammonium chloride (Aldrich 99.99%) in the stoichiometric ratio 1:1.1 at temperatures between 740 and 780 uC during 12 hours in sealed evacuated silica tubes. In a second step a temperature gradient of 100 uC was applied to the same reaction tube and HfNCl and ZrNCl were recrystallized by chemical vapour transport. Sodium intercalation reactions were performed by the treatment of HfNCl with Naphtyl-sodium solutions in tetrahydrofuran with concentrations between 0.025 M and 1 M. The intercalation reaction time was 24 hours and the molar Na:HfNCl ratios ranged between 0.5:1 and 50:1. Filling of the reaction tubes, intercalation reactions and handling of the products for subsequent characterization were performed in an argon filled glove box. Attempts to determine the sodium content by chemical analysis were hindered by the fact that some sodium de-intercalation was found to take place during washing of the samples. With comparative purposes, electrochemical lithium intercalation experiments were conducted both in HfNCl and ZrNCl in lithium cells as previously described. The cells were tested using a...

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Phase mixtures and staging in intercalated LixNbSe2

Cited by 54 publications

References 9 publications

A new intermediate intercalate in superconducting sodium-doped hafnium nitride chloride

A new intermediate intercalate in superconducting sodium-doped hafnium nitride chloride

Effects of Rb Intercalation on NbSe₂: Phase Formation, Structure, and Physical Properties

A New Intermediate Intercalate in Superconducting Sodium‐Doped Hafnium Nitride Chloride.

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Phase mixtures and staging in intercalated LixNbSe2

Cited by 54 publications

References 9 publications

A new intermediate intercalate in superconducting sodium-doped hafnium nitride chloride

A new intermediate intercalate in superconducting sodium-doped hafnium nitride chloride

Effects of Rb Intercalation on NbSe2: Phase Formation, Structure, and Physical Properties

A New Intermediate Intercalate in Superconducting Sodium‐Doped Hafnium Nitride Chloride.

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Effects of Rb Intercalation on NbSe₂: Phase Formation, Structure, and Physical Properties