Internal Vibrational Modes Research Articles

Enhanced electrical performance of LiMnPO4 by carbon coating for solid-state battery applications

High-energy ball milling was employed to fabricate LiMnPO4 coated with varying carbon ratios (3%wt, 7%wt, and 10%wt), using glucose as a carbon source. The process involved pre-milling of LiMnPO4 precursors, followed by granulation through high-energy ball milling at 270 rpm for 2 h, and subsequent calcination at 700 °C without an inert gas flow. XRD analysis discerned the phases and structure of LiMnPO4, confirming the successful attainment of a single-phase LiMnPO4 without impurities. Rietveld refinement of the XRD data elucidated the crystallographic details, affirming the material's orthorhombic olivine structure with precise lattice parameters, thereby underpinning the structural integrity essential for electrochemical applications. FE-SEM analysis revealed uniformly distributed semi-sphere particles, with sizes ranging from 130 nm for LM to 183 nm for LM-10%C. FTIR analysis delineated the internal modes of vibration in the olivine structure and verified the presence of carbon on the powder surface. Electrical measurements conducted within the frequency range of 20 Hz–100 kHz demonstrated an increase in electrical conductivity with an escalation in carbon concentration, ranging from 31 μΩ−1m−1 to 75 μΩ−1m−1 for 0%C and 10%C, respectively. A temperature-dependent study spanning 30–160 °C revealed stable electrical conductivity behavior for the samples, with a marginal increase observed at elevated temperatures.

Spontaneous and stimulated Raman scattering by the products of the interaction of lithium deuteride with the environment

The processes of spontaneous and multicomponent stimulated Raman scattering (SRS) in a polycrystal consisting of the products of the interaction of lithium deuteride crystals with air molecules are studied. The interaction of lithium deuteride with environmental molecules resulted in a solid polycrystalline mixture of LiOH, LiOD, LiOH·H2O, and Li2CO3 on the crystal surface. Excitation of the sample under study by the third harmonic of a picosecond repetitively pulsed YAG:Nd3+ laser made it possible to detect three Stokes and the second anti-Stokes SRS components with a Raman frequency ν = 3660 cm−1 corresponding to the valence breathing mode of the OH− ion. A feature of the obtained spectra is the smaller spectral half-width of the second and third Stokes components compared to the first. When the studied polycrystals were excited by picosecond radiation with a wavelength λ = 532 nm, two Stokes and one anti-Stokes SRS components corresponding to the internal symmetric vibrational mode of LiOH were detected. The excitation of SRS at the Raman frequency of the OH− vibration ν = 3660 cm−1 in solids is promising due to the high-frequency shift and high quality factor, and is also important for studying the strength of hydrogen bonds.

Studies on luminescence properties of self-activated SrMoO4 phosphor: Kinetic analysis

The structure, photoluminescence, thermoluminescence and optically stimulated luminescence of SrMoO4 phosphor and its kinetic analysis have been investigated. The SrMoO4 sample was prepared by the solid-state route. Rietveld refinement of XRD pattern confirms that the SrMoO4 is in a tetragonal structure with space group I41/a. The particles are agglomerated and their size is around 5.8 ± 1.2 µm confirmed by scanning electron microscopy results. The observed seven internal modes of vibration in the Raman spectrum indicate the synthesized SrMoO4 is in scheelite type. Photoluminescence (PL) shows a broad peak with maxima at 490 nm when excited at 288 nm. An electron paramagnetic resonance spectrum shows a signal at a g-factor of 2.17 and is assigned to Mo5+ ions. Thermoluminescence (TL) of SrMoO4 shows two peaks, a prominent one at 365 K and a secondary peak at 472 K measured at a heat rate of 1 K s−1. Thermal cleaning and Tm-Tstop analysis reveal five peaks associated with the glow curve. The kinetic parameters analyzed using various methods show 365 K peak follows the non-first order of kinetics and the activation energy of this peak is about 0.78 ± 0.04 eV. The CW-OSL response increases linearly with a dose from 10 to 100 Gy. The CW-OSL and LM-OSL of SrMoO4 phosphor irradiated with 100 Gy fitted for three decay components. The photoionization cross sections values are (8.25 ± 0.24) × 10–18, (9.47 ± 0.61) × 10–19 and (8.14 ± 0.82) × 10–19 cm2 for fast medium and slow components respectively. A comparison of TL and residual TL (TL recorded after CW-OSL) confirms the traps of TL and OSL are the same and may possibly be shallow traps.

Influence of the internal degrees of freedom of coronene molecules on the nonlinear dynamics of a columnar chain.

The nonlinear dynamics of a one-dimensional molecular crystal in the form of a chain of planar coronene molecules is analyzed. Using molecular dynamics, it is shown that a chain of coronene molecules supports acoustic solitons, rotobreathers, and discrete breathers. An increase in the size of planar molecules in a chain leads to an increase in the number of internal degrees of freedom. This results in an increase in the rate of emission of phonons from spatially localized nonlinear excitations and a decrease in their lifetime. Presented results contribute to the understanding of the effect of the rotational and internal vibrational modes of molecules on the nonlinear dynamics of molecular crystals.

A systematic study of rare‐earth ions size‐dependent structural phase transition from monazite to zircon‐type in rare earth chromates using Raman spectroscopy

AbstractRare earth chromates (RCrO4) undergo monazite to zircon‐type structural phase transition due to a decreased rare‐earth ion size. They also exhibit an intermediate mixed phase. However, there is no systematic study on the influence of structural distortion on their phononic behavior, which is quite sensitive to subtle environmental variations. A change in the room temperature phononic spectrum was studied in the family of RCrO4 compounds, where R was varied from La to Yb using Raman modes. With an increase in the atomic number from Nd to Yb for zircon‐type phases, the external translational and rotational modes were observed to shift towards lower and higher wavenumbers, respectively. At the same time, all internal vibrational modes shifted towards higher phonon energies. A comparison between Raman modes for monazite, intermediate, and zircon‐type RCrO4 phases showed a gradual shift in the internal modes towards a higher wavenumber. The confirmation of the change in Raman modes with the decreasing radius was found by comparing the rare‐earth elements in DyCrO4 and LaCrO4 with non‐rare‐earth elements in YCrO4.

Raman and Structural Characterization of Spinel Compound Zn8/5Al4/15TiO4

Microwave dielectric materials have been attracted enormous attention for their application in microwave communication. A new microwave dielectric material with composition Zn8/5Al4/15TiO4 was synthesized by conventional solid-state reaction method. The structure of Zn8/5Al4/15TiO4 was refined with the cubic P4332 space group (number of formula unit per unit cell, Z = 4). The Rietveld refinement study revealed the theoretical density ρ = 4.80 g/cm3 and lattice parameter a = 8.405 Å. This compound was crystallized in cubic spinel structure and 1:3 ordering was observed on the octahedral sites. Raman spectrum of the compound was collected at room temperature. Theoretical Factor group analysis for this compound predicts 40 Raman modes and 22 IR modes. However, experimentally 13 vibrational modes have been observed in the Raman spectrum which can be separated into internal TiO6 vibration and external rotation and translation TiO6 modes. Raman modes in the range of 500-800 cm-1 are assigned to internal vibrational modes.

Synthesis, structure, and Mössbauer spectroscopic studies on the heat-induced solid-phase redox reactions of hexakis(urea-O)iron(III) peroxodisulfate

Anhydrous hexakis(urea-O)iron(III)]peroxydisulfate ([Fe(urea-O)6]2(S2O8)3 (compound 1), and its deuterated form were prepared and characterized with single-crystal X-ray diffraction and spectroscopic (IR, Raman, UV, and Mössbauer) methods. Six crystallographically different urea ligands coordinate via their oxygen in a propeller-like arrangement to iron(III) forming a distorted octahedral complex cation. The octahedral arrangement of the complex cation and its packing with two crystallographically different persulfate anions is stabilized by extended intramolecular (N–H⋯O = C) and intermolecular (N–H⋯O–S) hydrogen bonds. The two types of peroxydisulfate anions form different kinds and numbers of hydrogen bonds with the neighboring [hexakis(urea-O)6iron(III)]3+ cations. There are spectroscopically six kinds of urea and three kinds (2 + 1) of persulfate ions in compound 1, thus to distinguish the overlapping bands belonging to internal and external vibrational modes, deuteration of compound 1 and low-temperature Raman measurements were also carried out, and the bands belonging to the vibrational modes of urea and persulfate ions have been assigned. The thermal decomposition of compound 1 was followed by TG-MS and DSC methods in oxidative and inert atmospheres as well. The decomposition starts at 130 °C in inert atmosphere with oxidation of a small part of urea (~ 1 molecule), which supports the heat demand of the transformation of the remaining urea into ammonia and biuret/isocyanate. The next step of decomposition is the oxidation of ammonia into N2 along with the formation of SO2 (from sulfite). The main solid product proved to be (NH4)3Fe(SO4)3 in air. In inert atmosphere, some iron(II) compound also formed. The thermal decomposition of (NH4)3Fe(SO4)3 via NH4Fe(SO4)2 formation resulted in α-Fe2O3. The decomposition pathway of NH4Fe(SO4)2, however, depends on the experimental conditions. NH4Fe(SO4)2 transforms into Fe2(SO4)3, N2, H2O, and SO2 at 400 °C, thus the precursor of α-Fe2O3 is Fe2(SO4)3. Above 400 °C (at isotherm heating), however, the reduction of iron(III) centers was also observed. FeSO4 formed in 27 and 75% at 420 and 490 °C, respectively. FeSO4 also turns into α-Fe2O3 and SO2 on further heating.Graphical abstract

Laser Cooling and Trapping of Rare-Earth-Doped Particles

This review focuses on optical refrigeration with the anti-Stokes fluorescence of rare-earth (RE)-doped low-phonon micro- and nanocrystals. Contrary to bulk samples, where the thermal energy is contained in internal vibrational modes (phonons), the thermal energy of nanoparticles is contained in both the translational motion and internal vibrational (phonons) modes of the sample. Much theoretical and experimental research is currently devoted to the laser cooling of nanoparticles. In the majority of the related work, only the translational energy of the particles has been suppressed. In this review, the latest achievements in hybrid optical refrigeration of RE-doped low-phonon micro- and nanoparticles are presented. Hybrid cooling permits the suppression of not only the translational energy of the RE-doped particles, but also their internal vibrational phonon thermal energy. Laser cooling of nanoparticles is not a simple task. Mie resonances can be used to enhance laser cooling with the anti-Stokes fluorescence of nanoparticles made of low-phonon RE-doped solids. Laser-cooled nanoparticles is a promising tool for fundamental quantum-mechanical studies, nonequilibrium thermodynamics, and precision measurements of forces.

Diagnosis of Dental Fluorosis Using Micro-Raman Spectroscopy Applying a Principal Component-Linear Discriminant Analysis

Dental fluorosis is an irreversible condition caused by excessive fluoride consumption during tooth formation and is considered a public health problem in several world regions. The objective of this study was to evaluate the capability of micro-Raman spectroscopy to classify teeth of different fluorosis severities, applying principal component analysis and linear discriminant analysis (PCA-LDA), and estimate the model cross-validation accuracy. Forty teeth of different fluorosis severities and a control group were analyzed. Ten spectra were captured from each tooth and a total of 400 micro-Raman spectra were acquired in the wavenumber range of 250 to 1200 cm−1, including the bands corresponding to stretching and bending internal vibrational modes ν1, ν2, ν3, and ν4 (PO43−). From the analysis of the micro-Raman spectra an increase in B-type carbonate ion substitution into the phosphate site of the hydroxyapatite as fluorosis severity increases was identified. The PCA-LDA model showed a sensitivity and specificity higher than 94% and 93% for the different fluorosis severity groups, respectively. The cross-validation accuracy was higher than 90%. Micro-Raman spectroscopy combined with PCA-LDA provides an adequate tool for the diagnosis of fluorosis severity. This is a non-invasive and non-destructive technique with promising applications in clinical and epidemiological fields.

X-ray diffraction and spectroscopic study of SrxCa1−xCO3: Implications for equilibrium Sr2+ incorporation and carbon/oxygen isotope fractionation in aragonite

Eight SrxCa1−xCO3 (0.2 < x < 0.9) solid solutions with orthorhombic aragonite structure were synthesized at P = 1.5 GPa and T = 1300 °C over 48 hours. Powder X-ray diffraction (XRD) analyses show that their unit-cell parameters and volumes increase systematically with increasing Sr2+ concentration, and the excess volume (ΔV) has been found to be insignificant at temperatures up to 700 K, or pressures up to 3 GPa. The Raman and Fourier-transform infrared (FTIR) spectra of these solid solutions show that all lattice and internal vibrational modes shift systematically to lower frequencies with increasing Sr2+ content, exhibiting a negative dependence of vibrational frequencies on the average mass of divalent cation for the aragonite-group carbonates in the order of aragonite > strontianite > witherite > cerussite. The vibrational contribution to the excess Gibbs free energy is constrained for the SrxCa1−xCO3 solid solution, whose miscibility gap shrinks at elevated temperatures and disappears above ~400 K. The calculated equilibrium Sr-Ca exchange coefficient (KDSr/Ca) between aragonite and seawater is systematically lower than the measured ones below ~80 °C, suggesting kinetic control on Sr partitioning at low temperatures. We also evaluate the metal cation effect on the carbon and oxygen isotope fractionations between aragonite-group carbonates and CO2 or H2O. Our results show that the 1000∙lnβ (where β is the reduced partition function ratio) for both carbon and oxygen isotope fractionations decrease linearly with increasing average atomic mass of the divalent cation in these aragonite-group carbonates, and the compositional effect on isotope fractionations can be treated as a linear function of Sr2+ concentration in the SrxCa1−xCO3 solid solution.

Energy transfer to the phonons of a macromolecule through light pumping

In the present paper we address the problem of the energy downconversion of the light absorbed by a protein into its internal vibrational modes. We consider the case in which the light receptors are fluorophores either naturally co-expressed with the protein or artificially covalently bound to some of its amino acids. In a recent work [Phys. Rev. X 8, 031061 (2018)], it has been experimentally found that by shining a laser light on the fluorophores attached to a protein the energy fed to it can be channeled into the normal mode of lowest frequency of vibration thus making the subunits of the protein coherently oscillate. Even if the phonon condensation phenomenon has been theoretically explained, the first step - the energy transfer from electronic excitation into phonon excitation - has been left open. The present work is aimed at filling this gap.

Synthesis and vibrational spectroscopy of [formula omitted] Tutton’s salt

The crystals of the Tutton’s salt are the promising material for the solar-blind technology. In this present work, single crystals of the Tutton’s salt family having empirical formula (NH4)2Co (Crx S1-xO4)2.6H2O (ACOCRSH), were grown by the slow thermal evaporation of the aqueous solution technique. These types of isomorphic inorganic materials belong to the monoclinic system with factor group symmetry C52h. The group factor analysis demonstrates that these types of crystals have total 234 normal modes of vibrations including three acoustic translational modes. The Raman spectroscopy measurements of the sample crystal were carried out in the range of 100−4000 cm−1, whereas the FTIR spectroscopy measurements of the sample crystal were taken place in the region between 400−4000 cm−1. In addition, the determination of the internal and external modes of vibrations of the [Co(H2O)6]2+ octahedral complex, NH4+, CrO42- and SO42- tetrahedra and H2O molecules from the experimental spectra and their assignments have been investigated rigorously.

Monitoring the evolution of intersite and interexciton coherence in electronic excitation transfer via wave-packet interferometry.

We detail an experimental strategy for tracking the generation and time-development of electronic coherence within the singly excited manifold of an energy-transfer dimer. The technique requires that the two monomers have nonparallel electronic transition-dipole moments and that these possess fixed orientations in space. It makes use of two-dimensional wave-packet interferometry (WPI or whoopee) measurements in which the A, B, C, and D pulses have respective polarizations e, e, e, and e'. In the case of energy-transfer coupling that is weak or strong compared to electronic-nuclear interactions, it is convenient to follow the evolution of intersite or interexciton coherence, respectively. Under weak coupling, e could be perpendicular to the acceptor chromophore's transition dipole moment and the unit vector e' would be perpendicular to the donor's transition dipole. Under strong coupling, e could be perpendicular to the ground-to-excited transition dipole to the lower exciton level and e' would be perpendicular to the ground-to-excited transition dipole to the upper exciton level. If the required spatial orientation can be realized for an entire ensemble, experiments of the kind proposed could be performed by either conventional four-wave-mixing or fluorescence-detected WPI methods. Alternatively, fluorescence-detected whoopee experiments of this kind could be carried out on a single energy-transfer dimer of fixed orientation. We exhibit detailed theoretical expressions for the desired WPI signal, explain the physical origin of electronic coherence detection, and show calculated observed-coherence signals for model dimers with one, two, or three internal vibrational modes per monomer and both weak and strong energy-transfer coupling.

Study of the vibrational properties of haloperidol under high-pressure

Haloperidol, with molecular formula C21H23ClFNO2, is a conventional antipsychotic drug used to relieve the symptoms of schizophrenia. Although its pharmacology has been extensively reported, only few studies focused on its vibrational features. In this work, Raman spectroscopy was used to investigate the vibrational properties of the haloperidol crystal under high-pressure conditions up to approximately 5.9 GPa. Our results showed changes in the low wavenumber bands accompanied by some changes in the internal vibrational modes, indicating the occurrence of a phase transition. Analysis of the Raman spectra shows phase transitions around 2.0 GPa and 4.2 GPa, with the disappearance and appearance of some modes in addition to discontinuities in the evolution of the frequencies of several normal modes of vibration. Such changes involved modes located in the region of external modes while others involved modes of the molecular skeleton and modes that participate in hydrogen bonds. At 4.2 GPa the changes were related to small conformational changes associated with hydrogen bonds and small deformations in the haloperidol molecules. At 2.0 GPa it was observed a change corresponding to the lattice modes, indicating a structural phase transition with conformational change.

Raman Scattering Studies of the Structural Phase Transitions in Single-Crystalline CH3NH3PbCl3.

Methylammonium lead trihalide perovskites CH3NH3PbX3 (X = Cl, Br, and I) have recently attracted huge attention as a promising candidate for highly efficient solar cell absorber materials. To understand the physical properties of halide perovskites, we investigated the CH3NH3PbCl3 single crystal by Raman scattering spectroscopy from 80 K to room temperature. Benchmarking the phonon modes and their Raman activities obtained by density functional calculations, we successfully assign the molecular vibrations of methylammonium in the frequency range from 400 to 3300 cm-1. In the temperature-dependent Raman scattering spectra, the internal vibrational modes of the CH3NH3+ cation are observed in the frequency range above 400 cm-1 and a number of peaks among them show characteristic changes that reflect the phase transition occurring at about 160 K in CH3NH3PbCl3. A noticeable Raman peak at 2900 cm-1 persists in a wide range of temperature, suggesting the existence of microcrystalline methylammonium chloride possibly left on the crystal surface from the growth process or spontaneously formed after synthesis.

Low-Frequency Vibrational Motions of Polystyrene in Carbon Tetrachloride: Comparison with Model Monomer and Dependence on Concentration and Molecular Weight

In this study, the low-frequency vibrational dynamics of polystyrene (PS) in CCl4 was investigated by femtosecond Raman-induced Kerr effect spectroscopy. Ethylbenzene (EBz) was also investigated as a model monomer of the polymer to elucidate the unique dynamical features of PS in solution. The broadened low-frequency spectrum of the PS/CCl4 in the frequency region below 150 cm-1 is significantly different from that of the EBz/CCl4. Difference spectra between the PS or EBz solutions and neat CCl4, normalized to an internal vibrational mode of CCl4, clearly show a much lower spectral intensity for the PS/CCl4 than the EBz/CCl4 in the low-frequency region below ca. 20 cm-1. This indicates that translational motions are suppressed in the PS/CCl4 compared to the EBz/CCl4. Moreover, the high-frequency motion at ca. 70 cm-1, mainly due to phenyl ring librations, occurs at higher frequency in PS (78 cm-1) than EBz (65 cm-1). In addition, the results of concentration-dependent experiments show that the first moment (M1) of the low-frequency difference spectra of both PS/CCl4 and EBz/CCl4 is almost independent of the concentration. The molecular weight dependence of the low-frequency spectrum in the PS/CCl4 shows that the M1 value of the low-frequency spectral band of PS shifts to higher frequencies when the molecular weight of PS increases up to Mw = ∼1000, which corresponds approximately to the decamer, and then remains constant upon further increasing the molecular weight.

Suppressing parametric instabilities in LIGO using low-noise acoustic mode dampers

Interferometric gravitational-wave detectors like LIGO need to be able to measure changes in their arm lengths of order $10^{-18}~$m or smaller. This requires very high laser power in order to raise the signal above shot noise. One significant limitation to increased laser power is an opto-mechanical interaction between the laser field and the detector's test masses that can form an unstable feedback loop. Such parametric instabilities have long been studied as a limiting effect at high power, and were first observed to occur in LIGO in 2014. Since then, passive and active means have been used to avoid these instabilities, though at power levels well below the final design value. Here we report on the successful implementation of tuned, passive dampers to tame parametric instabilities in LIGO. These dampers are applied directly to all interferometer test masses to reduce the quality factors of their internal vibrational modes, while adding a negligible amount of noise to the gravitational-wave output. In accordance with our model, the measured mode quality factors have been reduced by at least a factor of ten with no visible increase in the interferometer's thermal noise level. We project that these dampers should remove most of the parametric instabilities in LIGO when operating at full power, while limiting the concomitant increase in thermal noise to approximately 1%.

Preparation and Decay of a Single Quantum of Vibration at Ambient Conditions

A single quantum of excitation of a mechanical oscillator is a textbook example of the principles of quantum physics. Mechanical oscillators, despite their pervasive presence in nature and modern technology, do not generically exist in an excited Fock state. In the past few years, careful isolation of GHz-frequency nano-scale oscillators has allowed experimenters to prepare such states at milli-Kelvin temperatures. These developments illustrate the tension between the basic predictions of quantum mechanics that should apply to all mechanical oscillators existing even at ambient conditions, and the complex experiments in extreme conditions required to observe those predictions. We resolve the tension by creating a single Fock state of a vibration mode of a crystal at room temperature using a technique that can be applied to any Raman-active system. After exciting a bulk diamond with a femtosecond laser pulse and detecting a Stokes-shifted photon, the 40~THz Raman-active internal vibrational mode is prepared in the Fock state $|1>$ with $98.5\%$ probability. The vibrational state is read out by a subsequent pulse, which when subjected to a Hanbury-Brown-Twiss intensity correlation measurement reveals the sub-Poisson number statistics of the vibrational mode. By controlling the delay between the two pulses we are able to witness the decay of the vibrational Fock state over its $3.9$ ps lifetime at room temperature. Our technique is agnostic to specific selection rules, and should thus be applicable to any Raman-active medium, opening a new generic approach to the experimental study of quantum effects related to vibrational degrees of freedom in molecules and solid-state systems.

Vibrational studies, dielectric, and electrical conductivity in (Ba0.95Ca0.05)0.1(Ti0.8Sn0.2)0.1Na0.9Nb0.9O3 ferroelectric ceramic

(Ba0.95Ca0.05)0.1(Ti0.8Sn0.2)0.1Na 0.9Nb0.9O3 (BCNTSNO3) ferroelectric ceramic was synthesized by traditional solid-state method. Room temperature structural analysis, using X-ray diffraction data, confirmed the prepared ceramic purity with the existence of morphotropic phase boundary (MPB) which appears from tetragonal to orthorhombic symmetry with P4mm and Pmm2 space group, respectively. Temperature dependence of the dielectric measurement exhibited a ferroelectric–paraelectric transition at 540 K. Raman spectra were studied in the range of 50–1000 cm−1 as a function of temperature of 293 K–573 K. A detailed analysis of the frequency and half-width versus temperature introduces huge changes which are associated to the ferroelectric transitions originating from the internal vibrational modes of NbO6 octahedron. Electrical conductivity was carried out, using impedance spectroscopy, in the frequency and temperature range, 1 Hz–1 MHz and 500–600 K, respectively. Both impedance and modulus analysis exhibit the contribution of grain and grain boundary to the sample electrical response. To explain the impedance results, an equivalent circuit was proposed. The temperature dependence of the alternating current conductivity (σac) and characteristic relaxation time (τ) confirmed the observed ferroelectric phase transitions in the dielectric study. Moreover, temperature dependence of frequency exponent (s) is investigated to explain the conduction mechanism in the different regions. It was attributed to the correlated barrier-hopping model (CBH) in region (I) and (II).

Pressure-induced metallization, transition to the pyrite-type structure, and superconductivity in palladium disulfide PdS2

The pressure effect on crystal structures, lattice vibrations, and electrical transport properties of $\mathrm{Pd}{\mathrm{S}}_{2}$ and $\mathrm{NiS}{\mathrm{e}}_{2}$ were studied under high pressures of up to \ensuremath{\sim}50 GPa using Raman spectroscopy and electrical resistivity measurements. $\mathrm{Pd}{\mathrm{S}}_{2}$ undergoes semiconductor-to-metal transition at a pressure of \ensuremath{\sim}7 GPa without a structural phase transition. Structural transition to the pyrite-type phase occurs at a pressure of \ensuremath{\sim}16 GPa. Superconductivity emerges in the pyrite-type phase of $\mathrm{Pd}{\mathrm{S}}_{2}$ with a well-defined dome-shaped dependence of critical temperature of superconductivity on pressure, with a maximum value of 8.0 K at 37.4 GPa. Although this behavior is similar to that in isostructural $\mathrm{PdS}{\mathrm{e}}_{2}$, correlation with anomalous anion bond softening at critical temperature is not observed in $\mathrm{Pd}{\mathrm{S}}_{2}$ in contrast to $\mathrm{PdS}{\mathrm{e}}_{2}$. Conversely, the anion bond instability is observed by the softening of the $\mathrm{S}{{\mathrm{e}}_{2}}^{2\ensuremath{-}}$ internal vibrational Raman mode in pyrite $\mathrm{NiS}{\mathrm{e}}_{2}$ under pressure. Despite the persisting structural instability due to destabilization of $\mathrm{S}{{\mathrm{e}}_{2}}^{2\ensuremath{-}}$ dimers, $\mathrm{NiS}{\mathrm{e}}_{2}$ remains a normal nonsuperconducting metal.