Temperature-dependent Raman Spectra Research Articles

Reversible chromatic sensor fabricated by inkjet printing TCDA-ZnO on a paper substrate

A flexible reversible color change poly-(10,12-tricosadiynoic acid) TCDA-ZnO (2.5wt%) composite based chromatic sensor was successfully designed and fabricated by inkjet printing. Fabricated sensors showed good reversibility and stable chromatic properties with color transition temperature at 70°C. Attenuated Total Reflection (ATR) – Fourier Transform Infrared (FTIR) spectra show chelate formation between TCDA and ZnO. Temperature-dependent Raman spectra indicate that the blue-red phase of poly-TCDA-ZnO (2.5wt%) is thermally triggered at 70°C and the amorphous phase is formed near 120°C. An inkjet printed Quick Response (QR) code using poly TCDA-ZnO demonstrates a sensory functionality which can be incorporated in these codes.

Temperature dependence of Raman scattering in bulk 4H-SiC with different carrier concentration

Raman spectra of three bulk 4H-SiC wafers with different free carrier concentration were measured at temperature from 80 K to 873 K. As temperature increases, Raman peaks of most optical phonon modes show monotonous down shift. An anomalous non-monotonous variation with temperature, was observed in the A(1) longitudinal optical (LO) mode from doped samples. Two methods of theoretical fitting, one-mode (LO-plasma coupled (LOPC) mode) and two-mode (A(1)(LO) + LOPC) fitting, are employed to analyze this anomalous phenomenon. Theoretical simulations for temperature dependent Raman spectra by using two methods are critically examined. It turns out that one-mode method conforms well the experimental results, while two-mode method is untenable in physics. The non-monotonous variation of blue-red shifts with temperature for LOPC mode from doped 4H-SiC could be explained by the influence from ionization process of impurities on the process of Raman scattering. A quantitative description on temperature dependent Raman spectra for doped 4H-SiC is achieved, which matches well to experimental data.

RAMAN SPECTROSCOPY OF TEMPERATURE INDUCED EFFECTS IN FOUR CARBON ALLOTROPES

In this paper, we report strong variations in the Raman spectra of different carbon allotropes samples, for temperatures ranging from 83 K to 1123 K. The temperature dependence of D and G peak frequencies in the Raman spectrum of diamond, graphite, graphene, and carbon nanoparticles (CNPs) with 20 nm dot-size were investigated. These effects caused by temperature can be estimated from the changes in position [Formula: see text] and in linewidth of peak full width at half maximum (FWHM) G in the Raman spectrum of each sample. The broadening for each allotrope under the same conditions of temperature were: diamond ~ 4 cm-1, graphite ~ 50 cm-1, graphene ~ 5 cm-1 and nanoparticles ~ 7 cm-1. We also used scanning electron microscopy (SEM) to study the morphology and determine the size of the samples. According to the experimental data, the residual structural disorder and stress present in the samples are enhanced with temperature and responds for the observed changes in the Raman spectra. We present a systematic study of the temperature-dependent Raman spectra of four carbon allotropes.

Temperature Induced Structural Transformations and Gas Adsorption in the Zeolitic Imidazolate Framework ZIF-8: A Raman Study

Here we have used Raman spectroscopy to investigate molecular level changes in the zeolitic imidazolate framework ZIF-8 (a prototypical zeolite-like porous metal organic framework) as a function of temperature. Temperature dependent Raman spectra suggest that at low temperature the softening of the C-H stretching frequencies is due to the decrease in steric hindrance between the methyl groups of methyl imidazole. The larger separation between the methyl groups opens the window for increased nitrogen and methane uptake at temperatures below 153 K. The appearance of Raman bands at 2323 cm(-1) and 2904 cm(-1) at or below 153 K in ZIF-8 are characteristic signatures of the adsorbed nitrogen and methane gases respectively. Nanoscale ZIF-8 uptakes more molecules than bulk ZIF-8, and as a result we could provide evidence for encaged CO2 at 203 K yielding its Raman mode at 1379 cm(-1).

Thermally-induced loss of piezoelectricity in ferroelectric Na0.5Bi0.5TiO3–BaTiO3

The loss of piezoelectricity in ferroelectric sodium bismuth titanate (NBT) in solid solution with barium titanate ((1−x)NBT−xBT) is studied by means of thermal depoling and Raman spectroscopy. In the range 0≤x≤13%, the highest thermal stability of the piezoelectric coefficients is found in x=13%, for which a longitudinal piezoelectric coefficient of 118pC/N was nearly temperature-independent up to a maximum temperature of 165°C. The composition nearest the morphotropic phase boundary, x=6%, exhibited the lowest thermal depoling temperature of 107°C. Depoling of this composition is suggested to arise from a second order phase transition evidenced in the temperature-dependent Raman spectra.

Pressure and temperature dependence of Raman spectra and their anharmonic effects in Bi2Se3 single crystal

We report here on Raman spectroscopic studies of Bi2Se3 single crystal synthesized by chemical vapor transport technique as a function of pressure (0–12GPa) and temperature (80–300K). Polarized Raman experiments in the back-scattering configuration were performed to determine the position of the two dominant first-order Raman-active modes, Eg2 and A1g2 at around 132 and 174cm−1 respectively. High pressure Raman measurements provides the evidence that Bi2Se3 single crystal undergoes first order phase transition above 10GPa. Isobaric and isothermal mode Gruneisen parameter have been determined from the temperature and pressure dependent Raman spectra for both Raman active modes of Bi2Se3 single crystal. The analysis of the experimental data showed that the temperature dependencies of the phonon frequencies and linewidths were well described by considering the contributions from thermal expansion and lattice anharmonicity.

A polyene chain of canthaxanthin investigated by temperature-dependent resonance Raman spectra and density functional theory (DFT) calculations

We report on a temperature-dependent resonance Raman spectral characterization of the polyene chain of canthaxanthin. It is observed that all vibrational intensities of the polyene chain are inversely proportional to temperature, which is analyzed by the resonance Raman effect and the coherent weakly damped electron/lattice vibrations. The increase in intensity of the CC overtone/combination relative to the fundamental with temperature decreasing is detected and discussed in terms of electron/phonon coupling and the activation energy Uop. Moreover, the polyene chain studies using the density functional theory B3LYP/6-31G* level reveal a prominent peak at 1525 cm−1 consisting of two closely spaced modes that are both dominated by C=C stretching coordinates of the polyene chain.

Properties of the new electronic device material LaGdO3

AbstractThe room temperature crystal structure of potential high‐k dielectric LaGdO3 has been analyzed by X‐ray diffraction techniques and its structural evolution with temperature has been probed by Raman spectroscopy. Rietveld refinement of the ambient XRD data established the perfectly layered B‐type monoclinic crystal structure with a = 14.43 Å, b = 3.68 Å, c = 8.99 Å, and β = 100.57° which is further validated by the 21 (14 Ag and 7 Bg) Raman‐active vibrational modes with centro‐symmetric space group or C2/m. Atomic positions, coordination numbers, inter‐ionic lengths, etc. were derived using Rietveld analysis. All prominent Bragg peaks were successfully indexed. Temperature dependent Raman spectra of LaGdO3 from 80 to 1400 K were analyzed using the damped harmonic oscillator model. The softening and hardening of vibrational modes are reported. Above 900 K, disappearance of all high frequency modes (>600 cm−1) and merger of several mid frequency modes (between 200 and 500 cm−1) into two distinct modes was observed, a direct evidence of a possible structural phase transition from monoclinic to tetragonal/pseudocubic.

Anisotropic thermal expansion and anharmonic phonon behavior of mullite-type Bi2Ga4O9

We report the lattice thermal expansion and the temperature-dependent phonon behavior of the mullite-type Bi2Ga4O9 complex oxide. The thermal expansion was studied using composite data collected from powder and single crystal X-ray diffraction between 100K and 1273K. The lattice expansion occurred in the order of a<c<b. The anisotropic expansion behavior was monitored with respect to thermal expansion coefficients and the anisotropy factor. The volume thermal expansion was expressed using an extended Grüneisen first-order approximation to the zero-pressure equation of state; the model includes harmonic, quasi-harmonic and intrinsic anharmonic contributions to the internal energy as a function of temperature. The temperature dependent Raman spectra were collected from a single crystal between 78K and 1273K. The shift of the frequencies and the broadening of the line-widths with increasing temperature helped to analyze the anharmonicity and the thermal behavior of some phonons.

Temperature-Dependent Release of Guest Molecules and Structural Transformation of Hydroquinone Clathrates

The CO2-, CH4-, and CO2/CH4-loaded β-form hydroquinone (HQ) clathrates were synthesized by the gas-phase reaction between α-form HQ and high pressure gases. Temperature-dependent Raman spectra of guest-free, CO2-loaded, CH4-loaded, and CO2/CH4-loaded β-form HQ clathrates were measured in the temperature range 300–385 K at increments of 5 K. The CH4 molecules rapidly escaped from the β-form HQ clathrate in the temperature range 360–380 K, whereas the CO2 molecules were gradually released from the β-form HQ clathrate framework in the wide temperature range 300–380 K. It was also found that both CO2 and CH4 molecules were rapidly released from the CO2/CH4-loaded β-form HQ clathrate framework in the temperature range 360–380 K. However, all of the guest-free and guest-loaded β-form HQ clathrates were fully converted to the α-form HQ at the same temperature of 385 K. These results demonstrate the strong effect of temperature on both guest–host interactions and the stability of the framework structure.

Identification of Free OH and its Implication on Structural Changes of Liquid Water

The molecular structure of liquid water has been an outstanding issue for many years. The identification of free −OH holds the key in differentiating structure models for liquid water. By analyzing the relative changes of the intensity and depolarization ratio in temperature dependent Raman spectra, the occurrence of free −OH in liquid water is unambiguously determined. Furthermore, upon the increase of temperature from 5 °C to 85 °C, the structure of liquid water undergoes significant change, but the relative proportion of free −OH is considerably small and remains almost unchanged. This implies that the breaking of hydrogen bond from the tetrahedral structure prefers to occur at the site of the hydrogen acceptor. The energetic favoring of the structural change for liquid water is thus clearly revealed from experiments.

Direct Test of the Equivalency of Dynamic IR and Dynamic Raman Spectroscopies As Techniques for Observing Ultrafast Molecular Dynamics

We report the temperature-dependent infrared (IR) and Raman spectra of Fe(CO)3(η(4)-norbornadiene). This molecule undergoes carbonyl ligand site exchange on the vibrational time scale, and the effect of this exchange is observable as coalescence of the carbonyl bands in both the IR and Raman spectra. We outline a theory that we used to account for these effects and report simulations of the experimental spectra. We used these simulations to extract the carbonyl ligand exchange rates at various temperatures from the IR and Raman data. This data was used to calculate the activation energy for carbonyl exchange, yielding activation energies of 1.2 ± 0.2 and 1.4 ± 0.1 kcal/mol from the IR and Raman data, respectively. These activation energies are statistically identical and are consistent with previously reported values. This constitutes the first direct comparison between dynamic IR and Raman spectroscopies, and we find them to give identical results.

Thermal conductivity of 4H-SiC single crystals

Thermal diffusivity and specific heat of 4H-SiC crystals as a function of temperature are measured, respectively, from room temperature to 600 °C. The thermal conductivity normal to c-axis was calculated from the measured data for both N-type and V-doped semi-insulating (SI) 4H-SiC single crystals. The thermal conductivity of N-type sample normal to c axis is proportional to T−1.26. It is approximately 280 W/mK at the room temperature. For V-doped SI sample, the thermal conductivity is proportional to T−1.256 and it is about 347 W/mK at room temperature, bigger than that of N-type sample. For semiconductor materials, total thermal conductivity is the sum of the contributions of lattice and carrier thermal conductivities. Temperature dependent Raman spectrum showed that the life time of phonons for N-type sample is shorter than that for SI sample. Accordingly thermal conductivity contributions from both lattice and carrier components are relatively small for N-type sample.

Structural, magnetic, infrared and Raman studies of La0.8Sr x Ca0.2-x MnO3 (0 ≤ x ≤ 0.2)

We report the results of magnetic, X-ray powder diffraction, infrared and temperature dependent Raman spectra of the La0.8Sr x Ca0.2-x MnO3 (0 ≤ x ≤ 0.2) manganite. The structure refinement using the Rietveld method indicates that the partial substitution of strontium for calcium (for x ≥ 0.15) modifies the orthorhombic structure of the CaMnO3 perovskite towards a rhombohedral phase. Magnetic measurement confirms the increase in the Curie temperature from 180 K for La0.8Ca0.2MnO3 to 307 K for La0.8Sr0.2MnO3, respectively. It is argued that the substitution with the larger Sr2+ ion strengthens the double-exchange interaction and gives rise to the observed increase of transition temperatures. All manganites show two IR active vibrational modes around 400 and 600 cm−1. Moreover, when x ≤ 0.1, the absorption band around 400 cm−1 splits into two peaks. In addition, we have analyzed the frequencies and widths of the observed Raman modes as a function of temperature for all samples with various Sr content. The mode splitting is attributed to both magnetic ordering and large orthorhombic distortion in doped rhombohedral manganites.

Facile synthesis of carbon doped TiO2 nanowires without an external carbon source and their opto-electronic properties

The present study demonstrates a simple protocol for the preparation of one dimensional (1D) oxidized titanium carbide nanowires and their opto-electronic properties. The oxidized titanium carbide nanowires (Ox-TiC-NW) are prepared from TiC nanowires (TiC-NW) that are in turn synthesized from micron sized TiC particles using the solvothermal technique. The Ox-TiC-NW is characterized by X-ray diffraction, UV-Vis spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Raman spectroscopy. Thermal oxidation of TiC-NW yields carbon doped TiO2-NW (C-TiO2-NW), a simple methodology to obtain 1D C-TiO2-NW. Temperature dependent Raman spectra reveal characteristic bands for TiO2-NW. Electrical characterization of individual C-TiO2-NW is performed by fabricating a device structure using the focused ion beam deposition technique. The opto-electronic properties of individual C-TiO2-NW demonstrate visible light activity and the parameters obtained from photoconductivity measurements reveal very good sensitivity. This methodology opens up the possibility of using C-TiO2-NW in electronic and opto-electronic device applications.

Conformational and structural studies of ethynylcyclopentane from temperature dependent Raman spectra of xenon solutions, infrared spectra, and ab initio calculations

Variable temperature (−50 to −100°C) Raman spectra (3500–136cm−1) were recorded of ethynylcyclopentane, c-C5H9CCH in liquid xenon. The envelope-equatorial (Eq) conformer was determined more stable than envelope-axial (Ax) form with enthalpy difference of 94±9cm−1 (1.12±0.11kJ/mol) and 39±2% Ax conformer present at ambient temperature. The conformational stabilities have been predicted from ab initio calculations with basis sets up to aug-cc-pVTZ. From previously reported microwave rotational constants and ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r0 parameters are reported Eq [Ax] distances (Å) rCC=1.211(3) [1.211(3)], rCαCC=1.461(3) [1.467(3)], rCαCβ=1.542(3) [1.542(3)], rCβCγ=1.541(3) [1.542(3)], rCγCγ′=1.556(3) [1.555(3)] and angles (°) ∠CαCC=179.4(5) [179.9(5)], ∠CβCαCC=113.7(5) [111.5(5)], ∠CβCαCβ′=102.6(5) [102.1(5)], ∠CαCβCγ=103.7(5) [103.7(5)], ∠CβCγCγ′=106.0(5) [105.9(5)] and τCβCαCβ′Cγ′=40.8(5) [41.6(5)]. Vibrational assignments are reported, supported by ab initio predictions and results are discussed.

Lattice dynamics and dielectric functions of multiferroic BiFeO3/c-sapphire films determined by infrared reflectance spectra and temperature-dependent Raman scattering

Multiferroic BiFeO3 (BFO) films have been grown on c-sapphire substrates by pulsed laser deposition under different laser energies (EL). The X-ray diffraction and Raman spectra indicate that the films are polycrystalline and exhibit the single rhombohedral (R) phase. The crystal distortion becomes weaker with decreasing the EL, which is described by the ratio of c/a. It was found that different EL values also lead to the variation of the Bi/Fe ratio. Temperature-dependent Raman spectra were carried out to study the phonon mode evolution behaviors. The three A1 transverse optical (TO) phonon modes located at 219, 172, and 142cm−1 shift towards a lower energy side with the temperature due to thermal expansion, thermal disorder and the anharmonic effects of lattice. The E(TO) and three A1(TO) phonon frequencies slightly increase with increasing the EL of the growth condition, which results from the Bi vacancies, the changes of the length and intensity of BiO bonds and the local structure distortion in the FeO6 octahedra. The dielectric functions of the BFO films in the frequency range of 50–8000cm−1 have been extracted by fitting infrared reflectance spectra with the Lorentz multi-oscillator dispersion model. The variation trend of the dielectric functions with different EL can be observed and related to the packing density, surface roughness, and defect states. It was concluded that the EL corresponding to changing the c/a ratio has an obvious influence on the lattice vibrations and intraband transitions of the BFO films.

Raman spectroscopy and optical properties of nanocrystalline NaAl(WO4)2:Cr3+ powders prepared by co-precipitation/calcination method

In this paper, we report on the pure and Cr3+-doped NaAl(WO4)2 nanopowders prepared by the co-precipitation/calcination method. X-ray diffraction, Raman/infrared spectroscopy, reflectance and luminescence studies (UV–vis optical band gap) of the obtained NaAl(WO4)2 nanoparticles are reported. Additionally, room temperature Raman and IR spectra as well as temperature-dependent Raman spectra are reported for NaAl(WO4)2 single crystal and its respective Raman-active modes are reported. Raman and IR studies showed that vibrational modes have been modified in comparison with the bulk material, indicating that with decreasing particle size some weak structural changes are induced in monoclinic NaAl(WO4)2 lattice. Optical investigations reveal that local crystal fields around Cr3+ ions in NaAl(WO4)2 nanocrystallities are of intermediate strength. A competition between the 2E and broadband 4T2 emissions is observed in these nanopowders due to small energy separation between the 2E and 4T2 energy levels of the Cr3+ ions. The splitting of the 2E level in the nanoparticles is about 84cm−1, indicating small distortion of the octahedral environment of the chromium ions. In the promoting 2E phosphorescence vibrations of the WO4 tetrahedra are especially effective.

High Thermoelectric and Reversible p-n-p Conduction Type Switching Integrated in Dimetal Chalcogenide

The subject of the involved phase transition in solid materials has formed not only the basis of materials technology but also the central issue of solid-state chemistry for centuries. The ability to design and control the required changes in physical properties within phase transition becomes key prerequisite for the modern functionalized materials. Herein, we have experimentally achieved the high thermoelectric performance (ZT value reaches 1.5 at 700 K) and reversible p-n-p semiconducting switching integrated in a dimetal chalcogenide, AgBiSe(2) during the continuous hexagonal-rhombohedral-cubic phase transition. The clear-cut evidences in temperature-dependent positron annihilation and Raman spectra confirmed that the p-n-p switching is derived from the bimetal atoms exchange within phase transition, whereas the full disordering of bimetal atoms after the bimetal exchange results in the high thermoelectric performance. The combination of p-n-p switching and high thermoelectric performance enables the dimetal chalcogenides perfect candidates for novel multifunctional electronic devices. The discovery of bimetal atoms exchange during the phase transition brings novel phenomena with unusual properties which definitely enrich solid-state chemistry and materials science.

Conformational and structural studies of 2,2,2 trifluoroethylamine from temperature dependent Raman spectra of xenon solutions and ab initio calculations

Variable temperature (−60 to −100°C) studies of the Raman spectra (4000–300cm−1) of 2,2,2 trifluoroethylamine, F3CCH2NH2 dissolved in liquid xenon have been carried out. From these data both conformers have been identified and their relative stabilities obtained. The enthalpy difference has been determined to be 267±27cm−1 (3.19±0.32kJmol−1) with the trans conformer the more stable form. The percentage of the gauche conformer is estimated to be 35±3% at ambient temperature. The conformational stabilities have been predicted from ab initio calculations utilizing several different basis sets up to aug-cc-pVTZ for both MP2(full) and density functional theory calculations by the B3LYP method. By utilizing previously reported microwave rotational constants along with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r0 parameters have been obtained for the trans conformer. The determined heavy atom structural parameters are for the distances (Å): C1–C2=1.513(3), C2–N3=1.447(3), C1–F4=1.344(3), C1–F5,F6=1.347(3) and angles in degrees (°) ∠N3C2C1=115.2(5), ∠F4C1C2=111.4(5), ∠C2C1F5, F6=111.6(5), ∠F4C1F5=107.6(5), and ∠F51F6=106.9(5). Vibrational assignments have been provided for the observed bands which have been supported by MP2(full)/6-31G(d) ab initio calculations to predict harmonic force fields, frequencies, infrared intensities, Raman activities and depolarization ratios for both conformers. The results are discussed and compared to the corresponding properties of some similar molecules.