Platinum Carbide Research Articles

Spectroscopic characterization of chain-to-ring structural evolution in platinum carbide clusters

Metal carbides play an important role in catalysis and functional materials. However, the structural characterization of metal carbide clusters has been proven to be a challenging experimental target due to the difficulty in size selection. Here we use the size-specific photoelectron velocity-map imaging spectroscopy to study the structures and properties of platinum carbide clusters. Quantum chemical calculations are carried out to identify the structures and to assign the experimental spectra. The results indicate that the cluster size of the chain-to-ring structural evolution for the PtCn– anions occurs at n = 14, whereas that for the PtCn neutrals at n = 10, revealing a significant effect of charge on the structures of metal carbides. The greatest importance of these building blocks is the strong preference of the Pt atom to expose in the outer side of the chain or ring, exhibiting the active sites for catalyzing potential reactions. These findings provide unique spectroscopic snapshots for the formation and growth of platinum carbide clusters and have important implications in the development of related single-atom catalysts with isolated metal atoms dispersed on supports.

Elastic, mechanical, thermo-physical, and ultrasonic investigation in platinum carbide

A comprehensive study of elastic, mechanical, thermophysical and ultrasonic properties of novel platinum carbide (PtC) have been reported. The elastic constants, mechanical properties e.g. bulk modulus, shear modulus, Young’s modulus etc., direction dependent thermal and ultrasonic properties of PtC in rock-salt (RS-type) and wurtzite (WZ-type) structures are determined. Thermal properties e.g. thermal relaxation time, lattice thermal conductivity, specific heat per unit volume, crystal energy density, acoustic coupling constants, and ultrasonic attenuation were determined along different directions. In order to access the microstructural information and nature of material the direction dependent ultrasonic properties of PtC were correlated with other thermophysical properties. The elastic, mechanical, thermophysical and ultrasonic properties of wurtzite crystal structure have been reported for first time. All results reveal that PtC would favour wurtzite crystal phase. The compound is stiffer in wurtzite phase. The obtained results may be further explored for research and industrial applications.

Theoretical investigation of the structural stabilities, elastic properties and band structure characteristics of platinum carbide

ABSTRACTAb initio calculations based on the density functional theory within the full-potential linearized augmented plane wave method were carried out to investigate the structural stabilities of the different crystallographic phases, the pressure-induced phase transition and the electronic properties of the platinum carbide (PtC) compound. The zinc-blende (ZB), rock-salt (RS), cesium chloride (CsCl), wurtzite (WZ), nickel arsenide (NiAs), lead monoxide (PbO) and the tungsten carbide (WC) phases were considered. The exchange and correlation potential was treated by the generalized-gradient approximation using the Perde–Burke–Ernzerhof parameterization. The thermodynamic properties such as variation of the bulk modulus, lattice constant, heat capacity, thermal expansion and Debye temperature versus pressures and temperatures are investigated. The band structure results show the metallic character of the PtC compound in all the considered phases and the present study also shows that the PtC compound crystallizes in the ZB phase at ambient conditions. The theoretical transition pressures from the ZB to RS for the NiAs, PbO and CsCl transformations were also computed.

Structural and mechanical properties of platinum carbide.

Platinum carbide (PtC) was synthesized under extreme conditions and considered as a potential candidate for superhard materials. However, the unsettled issue concerning the structural identification has impeded the full understanding of its physical and chemical properties. Here, we examine by first-principles calculations the crystal structure under high pressure and ideal strength along several high-symmetry directions under large deformation. The current calculations reveal that the zinc blende structure is the thermodynamically stable phase, and the simulated X-ray diffraction data are in excellent agreement with the experimental pattern. Further strain-stress calculations indicate that anomalous fluctuating behaviors of ideal strength occur in PtC. These results are expected to broaden our understanding of the structural and mechanical properties for other potential superhard materials formed by heavy transition metals and light elements.

Structural Phase Transformation in SiC and PtC under Pressure

The study of pressure induced structural phase transition of silicon carbide and platinum carbide which crystallize in zinc blende structure (B3), has been carried out using the well described three body interaction potential model (TBIPM). Our present TBIP model consists of long range Coulombic, three body interaction and the short range overlap repulsive forces operative up to next nearest neighbor ions. These materials exhibit a first order phase transition from their ZnS (B3) to NaCl (B1) structure. The phase transition pressure for SiC and PtC are 94.5 GPa and 50GPa respectively.

The effect of the phase transition on the elasticity of cubic platinum carbide

A study of the high-pressure elastic properties of ideal stoichiometric platinum carbide (PtC) in the rock-salt (RS) and zinc-blende (ZB) structures was conducted using first-principles calculations based on density functional theory, in which we employ the generalized gradient approximation of the Perdew–Burke–Eruzerhof form together with plane-wave basis sets for expanding the crystal orbitals and periodic electron density. Our calculation shows that the recently synthesized compound PtC possess a high-bulk modulus value in the RS phase and the ZB phase is more stable. The investigation of the elastic stability under pressure indicated that the transition pressure from ZB to RS structure of PtC is about 30 GPa and the high-pressure RS phase is stable up to 100 GPa. Our conclusions are consistent with the other theoretical predictions but are reversed with the diamond anvil cell experimental results. Therefore, the experimental observation of the RS structure in PtC remains a puzzle and our study indicates that more experimental and theoretical works need to be performed to ascertain the true nature of the newly discovered PtC material. In addition, the pressure dependence of the bulk modulus K, the shear modulus G, the Young’s modulus E, the Poisson’s ratio υ, the Debye temperature Θ D, the compressional wave velocity V p, the shear wave velocity V s, and the elastic anisotropy factor A for the ZB and RS structures of PtC are all successfully obtained. Moreover, the pressure dependence of the longitudinal and the shear wave velocities in three directions [100], [110], and [111] for cubic PtC are also predicted for the first time.

First-principles investigations of elastic stability and electronic structure of cubic platinum carbide under pressure

The authors have presented a detailed investigation on the phase stabilities and electronic properties of ideal stoichiometric platinum carbide (PtC) in the rock-salt (RS) and zinc-blende (ZB) structures under high pressure. Theoretical calculations are performed using the first-principles pseudopotential density functional method, in which we employ the generalized gradient approximation (GGA) of the Perdew-Burke-Ernzerhof form and local density approximation (LDA) of Ceperly and Adler parameterized by Perdew and Zunger together with plane-wave basis sets for expanding the periodic electron density. Through a series of tests, such as the total energy as a function of volume, the Gibbs free energy as a function of pressure, the P-V equation of states, the elastic stabilities, and the electronic band structures of PtC with ZB and RS phases, we have confirmed that the recently synthesized compound PtC is crystallized in the ZB structure at zero pressure and that the RS structure is a high-pressure phase; the phase transition studied from the usual condition of equal enthalpies occurs at the pressures of 46.6 and 46.5 GPa for GGA and LDA calculations, respectively. Our conclusions are consistent with the theoretical prediction obtained from the full-potential linearized augmented plane-wave method, but are reversed with the DAC experimental results and other pseudopotential plane-wave theoretical results. Therefore, the experimental observation of the RS structure in PtC remains a puzzle, and our study indicates that further experimental and theoretical investigations need to be carried out to find the cause of the stability of the PtC.

Stable structure of platinum carbides: A first principles investigation on the structure, elastic, electronic and phonon properties

A comprehensive first principles study of structural, elastic, electronic, phonon and thermodynamical properties of novel metal carbide, platinum carbide (PtC) is reported within the density functional theory scheme. The ground state properties such as lattice constant, elastic constants, bulk modulus, shear modulus and finally the enthalpy of PtC in zinc blende (ZB) and rock-salt (RS) structures are determined. The energy band structure and electron density of states for the two phases of PtC are also presented. Of these phases zinc blende phase of PtC is found stable and phase transition from ZB to RS structure occurs at the pressure of about 37.58 GPa. The phonon dispersion curves and phonon DOS are also presented. All positive phonon modes in phonon dispersion curves of ZB-PtC phase indicate a stable phase for this structure. Within the GGA and harmonic approximation, thermodynamical properties are also investigated. All results reveal that the synthesized PtC would favor ZB phase. The compound is stiffer and ductile in nature.

Dynamical stability and high pressure phases of platinum carbide

Using the density-functional linear response method, we study the dynamical properties of ground state zinc-blende and high pressure NaCl phases of platinum carbide (PtC). The calculated phonon dispersion curve does not show any soft modes for all wave vectors, indicating the dynamic stability of the ground state zinc-blende phase. The high pressure rock-salt phase exhibits imaginary frequencies, practically along all directions of the Brillouin zone, which means that PtC cannot exist in the NaCl phase at least up to a high pressure of 100 GPa.

Theoretical study of ground state and high-pressure phase of platinum carbide

We report local density-functional calculations using the full-potential linearized muffin-tin orbital method (FP-LMTO) for platinum carbide (PtC) in the, rock-salt (B1), zinc-blende (B3), wurtzite (B4), nickel-arsenide (B8) and PbO (B10) structures. The ground state properties such as the equilibrium lattice constant, elastic constants, the bulk modulus and its pressure derivative of PtC in these phases are determined and compared with available experimental and theoretical data. Our calculations show that the ground state phase of PtC to be zinc-blende (B3) structure at zero pressure and the nickel-arsenide (B8) structure is a high-pressure phase. The transition pressures at which this compound undergoes the structural phase transition from (B3) to (B8) and from (B3) to (B1) are found to be 34.25 and 51.28 GPa, respectively. The highest bulk modulus values in the nickel-arsenide (B8), zinc-blende (B3), rock-salt (B1) and PbO (B10) structures indicate that PtC is a hard material.

The first principles study on PtC compound

We have studied structural, thermodynamic, elastic, and electronic properties of platinum carbide (PtC) in zinc-blende and rock-salt structures by performing ab initio calculations within the LDA approximations. Particularly, we have focused on the structural and the pressure dependence of elastic moduli and related quantities. The other basic key properties, such as the lattice constant, cohesive energy, the phase transition pressure, bulk modulus and its pressure derivative are also repeated and compared with the other available experimental and theoretical works.

First-principles study on the structural, elastic and electronic properties of platinum carbide

First-principles calculations are carried out to investigate the structural, elastic and electronic properties of the newly synthesized noble metal carbide of platinum carbide (PtC). We use the plane-wave basis pseudo-potential method, in which both the local-density approximation (LDA) and the generalized gradient approximation (GGA) implanted in the CASTEP code are employed. The ground state properties such as lattice constant, elastic constants, bulk modulus and the final enthalpy of PtC in rock-salt (RS) and zinc-blende (ZB) structure are determined and compared with available experimental data. A series of geometry optimization was performed at a fixed value of applied hydrostatic pressure up to 120 GPa for the two different structures to simulate the experimental procedure of measuring the equation of state (EOS). From the pressure–volume data, we observed that the compressibility behavior of PtC in the RS structure is exactly with that of experiment. All the results reveal that the synthesized PtC would like to take the RS structure under high-pressure, which is meta-stable. The energy band structure and electron densities of states (DOS) of the two types of PtC are also presented. From the total and partial DOS, we find that the covalent bond of the RS structure is weaker than that of the ZB structure, which confirms that the former structure is meta-stable. Furthermore, both the DOS and energy band patterns show that the new compound is metallic.

A high-pressure and high-temperature synthesis of platinum carbide

High-pressure synthesis is a powerful method for the preparation of novel materials with high elastic moduli and hardness. Additionally, such materials may exhibit interesting thermal, optoelectronic, semiconducting, magnetic, or superconducting properties. We report on the new high-pressure, high-temperature synthesis of platinum carbide. The experiments were performed in a laser-heated diamond anvil cell and data were collected using the synchrotron X-ray diffraction method at pressures >75 GPa at high-temperatures. The new platinum carbide has a rock-salt type structure, with space group Fm3m and cubic symmetry. It was confirmed to remain stable to at least 120 GPa. This structure is the same as that of other metal carbides reported in previous studies. After decompression, the new high-pressure phase was recoverable at ambient pressure. The Birch–Murnaghan equation of state for this new phase was determined from the experimental unit cell parameters, with K 0=301 (±15) GPa, and K′ 0=5.2 (±0.4).

Chemistry, microstructure, and electrical properties at interfaces between thin films of platinum and alpha (6H) silicon carbide (0001)

Thin films (4-1000 Å) of Pt were deposited via UHV electron beam evaporation at room temperature on monocrystalline, n-type α (6H)-SiC(0001) substrates and examined in terms of chemistry, microstructure, and electrical properties. The as-deposited contacts were polycrystalline and showed excellent rectifying behavior with low ideality factors (n < 1.1) and leakage currents of 5 × 10−8 A/cm2 at −10 V. The Schottky barrier height increased from 1.06 eV before annealing to 1.26 eV after successive 20 min anneals at 450, 550, 650, and 750 °C. In addition, the leakage currents decreased to 2 × 10−8 A/cm2 at −10 V. Interfacial reactions were not observed at annealing temperatures below 750 °C; above this temperature, Pt2Si and C precipitates were identified in the reaction zone.

A High Surface Area Platinum Catalyst Prepared from Uranium Platinum Carbide for the Electrochemical Oxidation of Methanol

A high surface area platinum catalyst has been prepared by the electrochemical processing of uranium platinum carbide. This Raney‐type catalyst has a roughness factor exceeding 3000. The methanol oxidation current at this catalyst was about 1.8 A/cm2 at 60°C and a polarization of 1.2 V. Due to the high activity of the catalyst, the inhibition of methanol oxidation at more positive potentials and the consequent hysteresis in the oxidation response were not observed. The preparation, characterization, and evaluation of this catalyst material are described.

Field emission study of VIII transition metals: III. Adsorption of ethylene and acetylene on Pt

Field emission microscope has been used to study the adsorption and decomposition of ethylene and acetylene on platinum surface. Adsorption of ethylene reduced the work function by 0.65 eV. The heat treatment of ethylene-covered surface at 480 K increased relatively the emission from the stepped regions about the (211) planes, suggesting that some polymerization reactions of adsorbed ethylene occur. Exposure to acetylene decreased the work function by 1.05 eV. The adsorption of acetylene was suggested to be mainly non-dissociative. On heating the ethylene- or acetylene-covered surface, the decomposition involving the breaking of C C and C H bonds was observed at 480–830 K, accompanying an increase of the work function. Carbon left after dehydrogenation formed a surface carbide at around 830 K. At higher temperatures, the carbide carbon aggregated into graphite crystallites. The crystallites concentrated toward the (110) planes above 1100 K and finally diffused into the bulk at 1300 K. The formation of platinum carbide near the surface layer was suggested to form a new catalytic site on the (110) plane. The obtained results were compared with the previous results of the Ni and Pd emitters to discuss the catalytic behavior for the hydrogenation of hydrocarbons on these metals.

A Technique for Weighing a Single Whisker

ABSTRACT Due to the extremely fine size of inorganic whiskers, it is very difficult to determine the mass or density of a single whisker or its fragment. Patashnick and Hemenway [1] described an oscillating fiber microbalance (and the basic theory involved) for the determination of particulate masses in the 10−5 to 10−11 g range. This communication reports a simplified version of the apparatus and the procedure used in our laboratories to determine the mass and density of fragments of single whiskers of α-A12O3, platinum, graphite, and boron carbide.