[Li@C60]PF6: Infrared spectra from 90K to 523K; Determination of the molar extinction coefficients and integrated molar absorptivity

Abstract

The molar extinction coefficient ε and the integrated molar absorptivity ψ values of all the mid-infrared and far-infrared absorption bands of [Li@C₆₀]⁺PF₆^- were determined in comparison to those of C₆₀. The dependence from temperature of all the infrared absorption bands of [Li@C₆₀]⁺PF₆^- was measured in the temperature range comprised from 523?K and 90?K and extrapolated to 0?K. Once again, the results were discussed in comparison to the C₆₀ analogous experimental results.     

Esr Study of C60 N- Anion Radicals in DMSO Solution

Abstract

With the aim to stabilize reduced C₆₀ molecules of solid fulleride as free anion radicals in solution, Na_xC₆₀ (x=l, 10) was dissolved in DMSO. The Na_xC₆₀ was chosen among the other alkali-metal fullerides due to the possibility to increase a number of intercalated Na atoms in a fee. lattice of C₆₀ A sufficiently high concentration of C₆₀ anion radicals of an order of magnitude larger than that usually achieved in solution by an electrochemical reduction was obtained. The sharp resonances with the linewidths of order of 0.1 G and with g=2.0004(6) ?2.0012(8) of the room temperature ESR spectra of fluid solution were assigned from mono- to pentaanions of C₆₀. An appearance of additional sharp peaks at g=2.0016–2.0019 in the spectra of solution of nominal Na₁₀C₆₀, but Na₁C₆₀, tentatively related to C₆₀ ^n- with n>6. The results of this study showed a simple approach in an accomplishment of highly concentrated solutions of free anion radicals C₆₀ ^n-, as well as in stabilization of the anion radicals with increased n. In this way a homogeneity of alkali metal intercalation and characteristics of the solvent will be important.     

The Rectification Studies on the P+-Ion Implanted C60/Si Films

Abstract

N-type doping of the C₆₀ films deposited on Si substrates has been achieved by 80 keV P⁺-ion implantation with doses of 2×10¹⁴ cm^?2 at room temperature. The heterostructures composed of the n-type doped C₆₀ films and n- or p-type Si(111), Si(100) substrates are studied in view of semiconductor heterojunctions. The rectification and other electrical characteristics of the P⁺-ion implanted n-C₆₀/n-(p-)Si heterostructures are disclosed by the current-voltage (I-V) measurements at room temperature. The n-C₆₀/p-Si heterostructures show stronger rectification than n-C₆₀/n-Si heterostructures and Si(111) substrates are found to be more suitable for forming n-C₆₀/Si heterostructures than Si(100) substrates.     

He+ ION BOMBARDMENT OF C60 FULLERENE: AN FT-IR AND RAMAN STUDY

ABSTRACT

C₆₀ fullerene films have been bombarded with He⁺ ions at 30?keV at room temperature in vacuum. The structural changes undergone by C₆₀ have been followed by both FT-IR and Raman spectroscopy. Raman spectroscopy was the most useful tool for this scope. It has been clearly discovered that at low radiation dose C₆₀ forms oligomers but at higher radiation doses it is converted into an amorphous carbonaceous matter. The implications of these results on the possible survival of C₆₀ fullerene in the interstellar space have been discussed briefly in connection with the previous results on the effects of various types of electromagnetic radiation over C₆₀.     

Near-Infrared Laser-Induced Decomposition of C60 Dissolved in Toluene

Abstract

In this paper we describe the efficient and substantial decomposition of C₆₀ in toluene solution, induced by moderate intensity (I = 20 - 55 MW cm^?2) near infrared (γ = 1064 nm) laser radiation. This behavior is surprising since both uncharged fullerene and toluene do not have any absorption bands at this wavelength. The decomposition efficiency and products are investigated with UV-Vis absorption spectrophotometry and high-performance liquid-chromatography (HPLC). Possible mechanisms of the fullerene decomposition are discussed.     

Comparative Investigation of Elastic Diffuse Neutron Scattering in C60 Powder

Abstract

C₆₀ powder samples of varying impurity content have been investigated by neutron scattering techniques. For Q > 2.5 Å^?1 (Q = transferred momentum) strong elastic diffuse scattering is found below T_c ~ 260 K providing evidence of static disorder in the low temperature phase. The elastic scattering increases on cooling from T_c to 150 K but remains virtually constant below this temperature. There is no marked dependence on the impurity level. For Q > 2.5 Å^?1 elastic diffuse scattering obeying a sin(QR)/(QR) law is observed both above and below the phase transition (R= radius of C₆₀ molecule). This scattering is nearly independent of temperature, however, depends strongly on the amount of impurities in the sample. In order to account for the unusually strong elastic diffuse scattering intensity model calculations have been performed which relate orientational disorder in C₆₀ to the elastic scattering observed in powder samples.     

Neutron bombardment of C60 and C70 fullerenes: A spectroscopic and calorimetric study

C₆₀ and C₇₀ fullerenes were neutron-bombarded to an integral dose of 3.28×10¹⁶ n cm^?2. After the neutron treatment the trichloromethane soluble fraction was determined spectrophotometrically and C₆₀ insoluble fraction was found at 3.8% while the insoluble fraction of C₇₀ 17.9%. The formation of the CHCl₃ insoluble fraction is due to polymerization and incipient amorphization of the neutron-bombarded fullerenes where C₇₀ appears more sensitive to radiation damage than C₆₀. Raman spectroscopy was used for the characterization of the irradiated fullerenes as well as electron spin resonance (ESR) and electronic absorption spectroscopy on solid samples. Differential scanning calorimetry (DSC) to 630°C was employed for the determination of the Wigner energy of the neutron-damaged fullerenes. The results are consistent with a higher level of radiation damage reached by C₇₀ in comparison to C₆₀ at the same neutron dose.     

Mass Spectrometry Study of C60 and C60-NiF2 Fluorination with Molecular Fluorine

Abstract

Fluorination of [60]fullerene and [60]fullerene-NiF₂(s) has been studied in situ by Knudsen cell mass spectrometry with admission of molecular fluorine. The fluorination processes were controlled in the temperature range 500 ? 800 K at molecular fluorine pressure 10^?4 ? 10^?5 atm. Temperature, time of fluorination and fluorine pressure were varied during the investigation. It was found that variation of these parameters did not lead to the selective fluorination. It was shown that NiF₂(s) significantly influences the composition of the product mixture: a large amount of nickel difluoride in the system suppresses the fluorination reaction while the presence of a small amount promotes the selective fluorination. C₆₀Fi₁₈ (50% in the gas phase) was produced in our experiments under the following conditions: 20 h, 720 K, P(F₂) = 2 10^?4 atm in the prefluorinated (inner surface covered with NiF₂(s) layer) Ni-reactor. An important point of the study was verification of the thermodynamic equilibrium in the system. It was concluded that the equilibrium is not established in the system under study, and the fluorination is governed by kinetic factors.     

Pressure dependence of superconductivity in Ba4C60

In Ba_xC₆₀ superconductivity (sc) at T_c=(6.8±0.2) K is associated with the x=4 phase. Here we present pressure studies of T_c of a Ba_xC₆₀ sample (dT_c/dp= –1.9 K/GPa) which exhibits a large volume fraction of the x=4 phase. In the alkali-fullerides K₆₀C₆₀ and Rb₃C₆₀ T_c is governed by the electronic density of states N(E_F) (T_c exp{–1/N(E_F)V}). The dependence of N(E_F) on volume can be approximated by N(E_F)=N₀ d _eff ³, where d_eff is the surface to surface distance of neighboured C₆₀-molecules. This relationship is corroborated by (T_C,d)-data of various compounds of the form A_3–xB_xC₆₀ (A: K, Rb; B: K, Rb, Cs; x2). Strong deviation from this behavior is found for the alkaline-fulleride superconductor Ba₄C₆₀. This deviation is attributed to the hybridization of alkaline-metal s-, d-states and C₆₀ -states.     

UNSTABLE PRODUCTS FROM THE OZONATION OF C60 IN SOLVENTS

The ozonation of a solution of C₆₀ in toluene results in the formation of several unstable compounds C₆₀X and C₆₀Y[1–5] which decay completely at room temperature within about 1 h. The products are oxides C₆₀O[6,6], C₆₀O₂[I], C₆₀O₂[II], and possibly an isomer of C₆₀O₃. The transformations are not due to oxidation by atmospheric oxygen but are spontaneous. The ozonation of a solution of C₆₀O[6,6] in toluene results in the formation of two unstable compounds C₆₀Z[1–2] which also decay completely to C₆₀O₂[I] and C₆₀O₂[II]. It is suggested that all unstable “parents” are ozonides.     

Reaction Kinetics of C60 Fullerene Ozonation

Abstract

It has been verified that the reaction between O₃ and C₆₀ follows the general second order reaction rate which is valid for all the reactions between ozone and unsaturated olefinic bonds: v = k[C?C][O₃]. The reaction rate constant k has been measured ≈(1.5 ± 0.3) × 10⁴ L mol^?1 s^?1. The value of this rate constant has the same order of magnitude of the rate constant measured for instance in the ozonation of 1,4‐diphenylbutadiene.     

Molecular Orientational Ordering in Solid C60

Abstract

Single-crystal X-ray diffraction studies of the orientational ordering in solid C₆₀ are reviewed. The temperature dependence of selected Bragg reflections was carefully examined, allowing to obtain original information on the first-order orientational ordering transition at T_o = 259K, the unusual behavior of both fundamental and superstructure reflections below T_o and the freezing in of the C₆₀ reorientations at T_g ≈ 85K. The diffuse intensity due to orientational disorder of the C₆₀ molecules at room temperature is found to be strongly modulated, both radially and azimuthally. showing that the molecular orientations are indeed correlated. The corresponding intensity distribution has been calculated within a mean-field theory for different microscopic models of inter molecular interactions. It should allow a better understanding of these interactions.     

X-Ray Diffraction Studies of the Recrystallization of C60-Based Polymers

Abstract

A time-dependent x-ray scattering study is presented of the kinetics of the C₆₀-based star polymer containing 6 urethane-connected polyether and the star model polymers containing 4, 3, and 2 urethane-connected polyether arms. By varying the temperature from 40°C to -40°C, the order-disorder phase transition (recrystallization) of the polymers has been observed. Two crystalline domains with the periodicities of 4.5±0.6 Å and 3.7±0.4 Å were detected. The domain sizes ranging from 70 Å to 250 Å, the transition temperatures from -15°C to 25°C and the maximum percentage of recrystallization from 13% to 34% increase as the number of polyether arms increases. The x-ray scattering peaks of the order phase grow up as I₁ +I₂(l - e^?t/t0), where I₁ and I₂ are the initial intensity and the proportional intensity modulus, respectively. The relaxation time t₀ of the order phase is varying as a power law with respect to the reduced temperature T_R(=(T - T_C)/T_C): t₀ = (35±10)·|T_R|^?1.42±0.07 seconds for the C₆₀-based star polymer containing 6 urethane-connected polyether; t₀ = (315 ± 64)·|T_R|^?1.68±0.08 seconds for the star model polymer containing 4 urethane-connected polyether arms.     

Electrical and Optical Properties of Ion Implanted C60

Abstract

Electrical studies (based on conductivity and thermopower) and optical studies have been performed on implanted C₆₀ thin films. In order to obtain the doping effect by charge transfer from alkali atoms to C₆₀ molecules or to large fragments (stemming from degradation effects), the optimization of implantation parameters leads to the values: E = 30keV, D  10¹⁵ions/cm², T=77K. The conductivity [sgrave] and the thennopower S reach the values: σ ? 10²ωcm^?1 and S ? -50μV/K.     

Catalytic 3D polymerization of C60

The present study addresses the problems of catalytic synthesis of C₆₀-based 3D polymers in the presence of carbon disulfide CS₂. It is shown that CS₂ lowers the pressure of fullerite 3D polymerization at room temperature. In particular, the pressure at which the 3D ultrahard fullerite C₆₀ phase is formed decreases from 18 GPa to 7 GPa. The catalyst plays no significant role at room temperature and low pressures up to 6 GPa. When the C₆₀ + CS₂ is heated to 1200 K, the pressure of the 3D C₆₀ polymerization is further reduced to 2–4 GPa. Based on the TEM data, we propose a 3D polymer structure based on C₆₀ obtained by the catalytic synthesis.     

Systeme Li0,5Ga2,5−xCrxO4 (0 ⩽ x ⩽ 2) : Correlations entre structure cristalline,proprietes optiques et spectre vibrationnel

The order-disorder transitions P4₃32 → Fd3m and F4?3m → Fd3m in the system Li_0,5Ga_2,5?xCr_xO₄ occur respectively for x = 1,25 and x = 1,75. The absorption spectra (d.r.s) disclose Cr³⁺ ions in Td symetry from x = 0,75 to x = 2 (ligand-field parameters of Cr³⁺ in A sites : Dq = 700 cm^?1, B = 500 cm^?1). Structure of Li_0,5Ga_0,875Cr_1,625 is established by means of X-ray and neutronic diffraction : Li⁺_0,24Ga³⁺_0,74Cr³⁺_0,02 [Li⁺_0,26Ga³⁺_0,135Cr³⁺_1,605] O^2?₄. Infrared and Raman spectra of ⁶Li_0,5Ga_2,5O₄ and ⁷Li_0,5Ga_2,5O₄ are reported. The IR spectra of ordered spinels (0 ? x ? 0,5 ; 1,75 < x ? 2) are discussed and partly assigned with the help of ⁶Li ? ⁷Li isotopic shifts.     

Surface Ionization Mass Spectrometric Studies of the Li/C60 System

Abstract

We have studied the Li/C₆₀ system by the surface ionization mass spectrometry. We have investigated a possibility of the Li@C₆₀ formation via the collisions between Li⁺and C₆₀ ^? ions in a plasma state, which was predicted by an ab initio molecular dynamics simulation. The LiC₆₀ complex was unambiguously observed. Our results do not allow direct determination of the LiC₆₀ structure but indicate that Li is inside the C₆₀ cage. We have determined the ionization potential of Li@C₆₀ complex (IP = 5.9 ± 0.1 eV), which agrees well with the calculated value of the IP of Li@C₆₀.     

Fullerene-containing C<Subscript>60</Subscript>-CdTe(CdSe) composite nanostructures

We have developed a technology for obtaining homogeneous films based on fullerene-containing C₆₀-CdTe and C₆₀-CdSe composites. The surface morphology of the initial films is characterized by an average lateral roughness size of about 150 nm. Annealing in a vacuum of 10^?5 Torr for 3 h showed that C₆₀-CdSe films are stable at temperatures up to T=180°C, while the same treatment of films of the (C₆₀)_1?x(CdTe)_x system with x<0.5 leads to the appearance of surface clusters of the semiconductor component with an average size of about 500 nm. The cluster density and size increase with the content of CdTe in the initial composite powder. The photoluminescence spectrum of a (C₆₀)_1?x(CdTe)_x film with x=0.5 upon annealing displays a dominating peak at 730 nm, which is indicative of a significant modification of the film structure as a result of this post-growth treatment. It is demonstrated that fullerene-containing composite network nanostructures with a lateral resolution up to 250 nm can be created by direct electron-beam lithography.     

Negative thermal expansion induced by intermetallic charge transfer

Abstract

Suppression of thermal expansion is of great importance for industry. Negative thermal expansion (NTE) materials which shrink on heating and expand on cooling are therefore attracting keen attention. Here we provide a brief overview of NTE induced by intermetallic charge transfer in A-site ordered double perovskites SaCu₃Fe₄O₁₂ and LaCu₃Fe_4?xMn_xO₁₂, as well as in Bi or Ni substituted BiNiO₃. The last compound shows a colossal dilatometric linear thermal expansion coefficient exceeding ?70 × 10^?6 K^?1 near room temperature, in the temperature range which can be controlled by substitution.     

A Study of Interaction of Dopants in C60: Doping Alkali-Halogen-Alkali into C60 in Successive Steps

It is well established that for an alkali-doped C₆₀ sample to be superconducting, the oxidation state C ^3– ₆₀ must be satisfied. It has been found previously that T _c is proportional to crystal parameter a in a face-centered cubic (fcc) structure. It is thus desirable to intercalate the largest possible size of molecule that can contribute one electron into every interstitial space. The successful process of such doping depends on our understanding the interaction among the dopants and C₆₀. We introduce a fabrication scheme of three steps successive doping using alkali (A) and halogen (H) elements along this line. While A ₃C₆₀ is superconducting, A _3–x (AH) _x C₆₀ was found to be non-superconducting in the second step and the sample became superconducting again after doping with A, leading to stoichiometric ratio of A _3–x (AH) _x A _x C₆₀. We present an explanation based on interaction among dopants and C₆₀ and analyze the process of ionization of dopants, which is consistent with our experimental finding reported here.