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Zinc phosphide (Zn3P2) is an II-V compound semiconductor with promising photovoltaic and thermoelectric applications. Its complex structure is susceptible to facile defect formation, which plays a key role in further optimization of the material. Raman spectroscopy can be effectively used for defect characterization. However, the Raman tensor of Zn3P2, which determines the intensity of Raman peaks and anisotropy of inelastic light scattering, is still unknown. In this paper, we use angle-resolved polarization Raman measurements on stoichiometric monocrystalline Zn3P2 thin films and first-principle calculations to obtain Raman tensor of Zn3P2. This has allowed determination of the Raman tensor elements characteristic for the A1g, B1g and B2g vibrational modes. These results have been compared with the theoretically obtained Raman tensor elements and simulated Raman spectra from the lattice-dynamics calculations using first-principles force constants. Excellent agreement is found between the experimental and simulated Raman spectra of Zn3P2 for various polarization configurations, providing a platform for future characterization of the defects in this material.

Predictive synthesis-structure-property relationships are at the core of materials design for novel applications. In this regard, correlations between the compositional stoichiometry variations and functional properties are essential for enhancing the performance of devices based on these materials. In this work, we investigate the effect of stoichiometry variations and defects on the structural and optoelectronic properties of monocrystalline zinc phosphide (Zn

There is currently an emerging drive towards computational materials design and fabrication of predicted novel materials. One of the keys to developing appropriate fabrication methods is determination of the composition and phase. Here we explore the FeGe system and establish reference Raman signatures for the distinction between FeGe hexagonal and cubic structures, as well as FeGe2 and Fe2Ge3 phases. The experimental results are substantiated by first principles lattice dynamics calculations as well as by complementary structural characterization such as transmission electron microscopy and X-ray diffraction, along with magnetic measurements.

Zinc phosphide (Zn3P2) is a II–V compound semiconductor with promising photovoltaic and thermoelectric applications. Its complex structure is susceptible to facile defect formation, which plays a key role in further optimization of the material. Raman spectroscopy can be effectively used for defect characterization. However, the Raman tensor of Zn3P2, which determines the intensity of Raman peaks and anisotropy of inelastic light scattering, is still unknown. In this paper, we use angle-resolved polarization Raman measurements on stoichiometric monocrystalline Zn3P2 thin films to obtain the Raman tensor of Zn3P2. This has allowed determination of the Raman tensor elements characteristic for the A1g, B1g and B2g vibrational modes. These results have been compared with the theoretically obtained Raman tensor elements and simulated Raman spectra from the lattice-dynamics calculations using first-principles force constants. Excellent agreement is found between the experimental and simulated Raman spectra of Zn3P2 for various polarization configurations, providing a platform for future characterization of the defects in this material., Raman tensor of zinc phosphide (Zn3P2) is determined using angle-resolved polarization Raman measurements and first principles calculations. These results provide a platform for future characterization of the defects in this material.

AgGaGeS4 is an emerging material with promising nonlinear properties in the near- and mid-infrared spectral ranges. Here, the experimental phonon spectra of AgGaGeS4 single crystals synthesized by a modified Bridgman method are presented. The infrared absorption spectra are reported. They are obtained from the fitting of reflectivity to a model dielectric function comprising a series of harmonic phonon oscillators. In the Raman spectra, several modes are registered, which were not detected in previous works. The analysis of the experimental vibrational bands is performed on the basis of a comparison with reported data on structurally related binary, ternary, and quaternary metal chalcogenides. The temperature dependence of the Raman spectra between room temperature and 15 K is also investigated.

Ternary (I–III–VI) and quaternary (I–II–IV–VI) metal-chalcogenides like CuInS2 or Cu2ZnSn(S,Se)4 are among the materials currently most intensively investigated for various applications in the area of alternative energy conversion and light-emitting devices. They promise more sustainable and affordable solutions to numerous applications, compared to more developed and well understood II–VI and III–V semiconductors. Potentially superior properties are based on an unprecedented tolerance of these compounds to non-stoichiometric compositions and polymorphism. However, if not properly controlled, these merits lead to undesirable coexistence of different compounds in a single polycrystalline lattice and huge concentrations of point defects, becoming an immense hurdle on the way toward real-life applications. Raman spectroscopy of phonons has become one of the most powerful tools of structural diagnostics and probing physical properties of bulk and microcrystalline I–III–VI and I–II–IV–VI compounds. The recent explosive growth of the number of reports on fabrication and characterization of nanostructures of these compounds must be pointed out as well as the steady use of Raman spectroscopy for their characterization. Interpretation of the vibrational spectra of these compound nanocrystals (NCs) and conclusions about their structure can be complicated compared to bulk counterparts because of size and surface effects as well as emergence of new structural polymorphs that are not realizable in the bulk. This review attempts to summarize the present knowledge in the field of I–III–VI and I–II–IV–VI NCs regarding their phonon spectra and capabilities of Raman and IR spectroscopies in the structural characterizations of these promising families of compounds.

Cu-Zn-Sn-Te (CZTTe) is an inexpensive quaternary semiconductor that has not been investigated so far, unlike its intensively studied CZTS and CZTSe counterparts, although it may potentially have desirable properties for solar energy conversion, thermoelectric, and other applications. Here, we report on the synthesis of CZTTe nanocrystals (NCs) via an original low-cost, low-temperature colloidal synthesis in water, using a small-molecule stabilizer, thioglycolic acid. The absorption edge at about 0.8–0.9 eV agrees well with the value expected for Cu2ZnSnTe4, thus suggesting CZTTe to be an affordable alternative for IR photodetectors and solar cells. As the main method of structural characterization multi-wavelength resonant Raman spectroscopy was used complemented by TEM, XRD, XPS as well as UV-vis and IR absorption spectroscopy. The experimental study is supported by first principles density functional calculations of the electronic structure and phonon spectra. Even though the composition of NCs exhibits a noticeable deviation from the Cu2ZnSnTe4 stoichiometry, a common feature of multinary NCs synthesized in water, the Raman spectra reveal very small widths of the main phonon peak and also multi-phonon scattering processes up to the fourth order. These factors imply a very good crystallinity of the NCs, which is further confirmed by high-resolution TEM.

Magnetic and crystallographic transitions in the Cairo pentagonal magnet ${\mathrm{Bi}}_{2}{\mathrm{Fe}}_{4}{\mathrm{O}}_{9}$ are investigated by means of infrared synchrotron-based spectroscopy as a function of temperature (20--300 K) and pressure (0--15.5 GPa). One of the phonon modes is shown to exhibit an anomalous softening as a function of temperature in the antiferromagnetic phase below 240 K, highlighting spin-lattice coupling. Moreover, under applied pressure at 40 K, an even larger softening is observed through the pressure-induced structural transition. Lattice dynamical calculations reveal that this mode is indeed very peculiar as it involves a minimal bending of the strongest superexchange path in the pentagonal planes, as well as a decrease in the distances between second-neighbor irons. The latter confirms the hypothesis made by Friedrich et al., [J. Phys.: Condens. Matter 24, 145401 (2012)] about an increase in the oxygen coordination of irons being at the origin of the pressure-induced structural transition. As a consequence, one expects a new magnetic superexchange path that may alter the magnetic structure under pressure.

Earth-abundant and low-cost semiconductors, such as zinc phosphide (Zn

Optical spectroscopy, x-ray diffraction measurements, density functional theory (DFT), density functional theory + embedded dynamical mean-field theory ($\mathrm{DFT}+eDMFT$), and crystal-field calculations have been used to characterize structural and electronic properties of hexagonal ${M}_{2}{\mathrm{Mo}}_{3}{\mathrm{O}}_{8}$ $(M=\mathrm{Fe},\mathrm{Mn})$ polar magnets. Our experimental data are consistent with the room-temperature structure belonging to the space group $P{6}_{3}mc$ for both compounds. The experimental structural and electronic properties at room temperature are well reproduced within $\mathrm{DFT}+eDMFT$ method, thus establishing its predictive power in the paramagnetic phase. With decreasing temperature, both compounds undergo a magnetic phase transition, and we argue that this transition is concurrent with a structural phase transition (symmetry change from $P{6}_{3}mc$ to $P{6}_{3}$) in the Fe compound and an isostructural transition (no symmetry change from $P{6}_{3}mc$) in the Mn compound.

Lattice dynamic properties of the tetragonal modification of ZnP

In this report, we describe a unique roll-to-roll plasma-enhanced chemical vapor deposition (R2R-PECVD) technique to grow high-quality single-crystalline-like Ge films on flexible metal foils, an important advancement towards scalable processing of epitaxial Ge films at low-cost. Ion-beam assisted deposition was used to create single-crystalline-like substrate templates to enable epitaxial growth of Ge films. The Ge films were highly (004) oriented, biaxially-textured and showed remarkable crystalline quality, equivalent to single-crystal Ge wafers. Subsequently, the Ge films on metal foils were used as substrates to fabricate flexible GaAs single-junction solar cell by metal-oxide chemical vapor deposition (MOCVD). The champion device showed efficiency of 11.5%, and the average efficiency of four devices was 8% at 1 sun, the highest reported on GaAs PV directly deposited on alternative flexible substrates. Devices made on CVD-Ge film exhibited significantly improved performance compared to the ones grown on sputtered Ge films. Scalable production of inexpensive and flexible epi-Ge films will not only be useful for developing low-cost and high-performance III–V solar cells, but also for emerging flexible electronic devices applications.

A skyrmion state in a noncentrosymmetric helimagnet displays topologically protected spin textures with profound technological implications for high-density information storage, ultrafast spintronics, and effective microwave devices. Usually, its equilibrium state in a bulk helimagnet occurs only over a very restricted magnetic field–temperature phase space and often in the low-temperature region near the magnetic transition temperature T(c). We have expanded and enhanced the skyrmion phase region from the small range of 55 to 58.5 K to 5 to 300 K in single-crystalline Cu(2)OSeO(3) by pressures up to 42.1 GPa through a series of phase transitions from the cubic P2(1)3, through orthorhombic P2(1)2(1)2(1) and monoclinic P2(1), and finally to the triclinic P1 phase, using our newly developed ultrasensitive high-pressure magnetization technique. The results are in agreement with our Ginzburg–Landau free energy analyses, showing that pressures tend to stabilize the skyrmion states and at higher temperatures. The observations also indicate that the skyrmion state can be achieved at higher temperatures in various crystal symmetries, suggesting the insensitivity of skyrmions to the underlying crystal lattices and thus the possible more ubiquitous presence of skyrmions in helimagnets.

A metastable germanium allotrope, Ge(oP32), was synthesized as polycrystalline powders and single crystals from the mild-oxidation/delithiation of Li7Ge12 in ionic liquids. Its crystal structure, from single crystal X-ray diffraction ( Pbcm, a = 8.1527(4) A, b = 11.7572(5) A, c = 7.7617(4) A), features a complex covalent network of 4-bonded Ge, resulting from a well-ordered topotactic oxidative condensation of [Ge12]7- layers. It is a diamagnetic semiconductor ( Eg = 0.33 eV), and transforms exothermically and irreversibly to α-Ge at 363 °C. This demonstrates the potential of ionic liquids as reactive media in the mild oxidation of Zintl phases to new highly crystallized modifications of elements and simple compounds.

Diamond anvil cell techniques, synchrotron-based infrared and Raman spectroscopies, and lattice dynamics calculations are combined with prior magnetic property work to reveal the pressure–temperature phase diagram of Co[N(CN)2]2. The second-order structural boundaries converge on key areas of activity involving the spin state exposing how the pressure-induced local lattice distortions trigger the ferromagnetic → antiferromagnetic transition in this quantum material.

This work presents a comprehensive analysis of the structural and vibrational properties of the kesterite Cu2ZnSnS4 (CZTS, I4 space group) as well as its polymorphs with the space groups P42c and P42m, from both experimental and theoretical point of views. Multiwavelength Raman scattering measurements performed on bulk CZTS polycrystalline samples were utilized to experimentally determine properties of the most intense Raman modes expected in these crystalline structures according to group theory analysis. The experimental results compare well with the vibrational frequencies that have been computed by first-principles calculations based on density functional theory. Vibrational patterns of the most intense fully symmetric modes corresponding to the P42c structure were compared with the corresponding modes in the I4 CZTS structure. The results point to the need to look beyond the standard phases (kesterite and stannite) of CZTS while exploring and explaining the electronic and vibrational properties ...

Single crystals of orthorhombic wurtzstannite Cu2ZnSiS4 (space group Pmn21 or C 2 υ 7 ) were synthesized by the chemical vapor transport method. Lattice dynamics of these crystals is studied experimentally by the low temperature polarized Raman scattering. Mode assignment to the specific lattice eigenmodes is performed based on a detail comparison with the results of density functional lattice dynamics calculations. Good agreement between theoretical and experimental mode frequencies is established.

Earth-abundant and environmentally friendly semiconductors offer a promising path toward low-cost mass production of solar cells. A critical aspect in exploring new semiconducting materials and demonstrating their enhanced functionality consists in disentangling them from the artifacts of defects. Nanowires are diameter-tailored filamentary structures that tend to be defect-free and thus ideal model systems for a given material. Here, an additional advantage is demostrated, which is the determination of the band structure, by performing high energy and spatial resolution electron energy-loss spectroscopy in aloof and inner beam geometry in a scanning transmission electron microscope. The experimental results are complemented by spectroscopic ellipsometry and are excellently correlated with first principles calculations. This study opens the path for characterizing the band structure of new compounds in a non-destructive and prompt manner, strengthening the route of new materials discovery.

Spectrally-selective solar absorber is required to be thermally stable at high operational temperature. However the currently available absorbers aren't stable beyond 700 °C. Here we explore a new absorber with cermet of TiN in SiO2 on LaAlO3 substrate that can be used for long term at 700 °C. The optimized cermets contain TiN with volume fraction of 60% and 65% as sun-light absorption media, SiO2 as anti-reflection coating (ARC), and tungsten (W) as infrared (IR) reflection layer. The absorbers demonstrate an absorptance higher than ~95% before annealing and ~94% after annealing at 700 °C, which will be useful for especially concentrated solar applications.

The structures of two trigonal-rhombohedral CaSi2 polymorphs (space group R3m) were studied by X-ray diffraction and polarized Raman scattering spectroscopy. Raman-active even-parity vibrational modes of A1g and Eg are unambiguously identified and assigned to the specific lattice eigenmodes. Experimental data are found to be in very good agreement with those predicted by density functional theory lattice dynamics calculations. The transformation of 6R structural modification of CaSi2 into its 3R polymorph, by high-temperature annealing in vacuum is also reported.

Nanocrystalline Zn2SnO4 powders doped with Eu3+ ions were synthesized via a mechanochemical solid-state reaction method followed by postannealing in air at 1200 °C. X-ray diffraction (XRD), energy-dispersive X-ray (EDX), and Raman and photoluminescence (PL) spectroscopies provide convincing evidence for the incorporation of Eu3+ ions into the host matrix on noncentrosymmetric sites of the cubic inverse spinel lattice. Microstructural analysis shows that the crystalline grain size decreases with the addition of Eu3+. Formation of a nanocrystalline Eu2Sn2O7 secondary phase is also observed. Luminescence spectra of Eu3+-doped samples show several emissions, including narrow-band magnetic dipole emission at 595 nm and electric dipole emission at 615 nm of the Eu3+ ions. Excitation spectra and lifetime measurements suggest that Eu3+ ions are incorporated at only one symmetry site. According to the crystal field theory, it is assumed that Eu3+ ions participate at octahedral sites of Zn2+ or Sn4+ under a weak cr...

The crystal structure of CuZnSiSe semiconductor, grown by the chemical vapor transport method, was determined by the powder and single-crystal X-ray diffraction and shown to be orthorhombic wurtzstannite (space group P mn2). Lattice dynamics of CuZnSiSe is studied by the low-temperature off-resonant polarized and resonant Raman scattering. Out of the total 45 optical vibrational modes allowed by the symmetry, 37 are observed in the spectra and are assigned to the specific lattice eigenmodes based on their polarization properties and a comparison of frequencies with the results of density functional lattice dynamics calculations. Good agreement between theoretical and experimental mode frequencies is established. The vibrational patterns for the most intense spectral lines in experimental spectra as well as pronounced resonant enhancement of Si-related modes are discussed.

We have synthesized Ba2XCu(OH)[V2O7] with X=Cl, Br by hydrothermal methods. The isotypic structures (Pnma, Z=4, a≈15.1 A, b≈6.1 A, c≈9.6 A) contain distorted hexagonal layers of Ba and X in a BN-type arrangement. Each halide is further coordinated by one out-of plane Ba atom in an alternate up-down fashion resulting in an overall Ba 2 X 3 + ∞ 2 structural feature. The planar Ba–X hexagonal rings are centered by divanadate groups in an eclipsed orientation. Edge-sharing chains of CuO 2/2 (OH) 2/2 O 2/1 5 - ∞ 1 complement the structure. The magnetic properties are associated with the magnetic Cu2+ ions and can be described as an antiferromagnetic quasi 1D S=1/2 Heisenberg system. Confirmation is obtained from both magnetic and specific heat measurements. Furthermore, lattice dynamics are studied by DFT methods, IR, and Raman spectroscopy.

Earth-abundant and low-cost semiconductors, such as zinc phosphide (Zn3P2), are promising candidates for the next generation photovoltaic applications. However, synthesis on commercially available substrates, which favors the formation of defects, and controllable doping are challenging drawbacks that restrain device performance. Better assessment of relevant properties such as structure, crystal quality and defects will allow faster advancement of Zn3P2, and in this sense, Raman spectroscopy can play an invaluable role. In order to provide a complete Raman spectrum reference of Zn3P2, this work presents a comprehensive analysis of vibrational properties of tetragonally-structured Zn3P2 (space group P42/nmc) nanowires, from both experimental and theoretical perspectives. Low-temperature, high-resolution Raman polarization measurements have been performed on single-crystalline nanowires. Different polarization configurations have allowed selective enhancement of A1g, B1g and Eg Raman modes, while B2g modes were identified from complementary unpolarized Raman measurements. Simultaneous deconvolution of all Raman spectra with Lorentzian curves has allowed identification of 33 peaks which have been assigned to 34 (8 A1g + 9 B1g + 3 B2g + 14 Eg) out of the 39 theoretically predicted eigenmodes. The experimental results are in good agreement with the vibrational frequencies that have been computed by first-principles calculations based on density functional theory. Three separate regions were observed in the phonon dispersion diagram: (i) low-frequency region (−1) which is dominated by Zn-related vibrations, (ii) intermediate region (210–225 cm−1) which represents a true phonon gap with no observed vibrations, and (iii) high-frequency region (>225 cm−1) which is attributed to primarily P-related vibrations. The analysis of vibrational patterns has shown that non-degenerate modes involve mostly atomic motion along the long crystal axis (c-axis), while degenerate modes correspond primarily to in-plane vibrations, perpendicular to the long c-axis. These results provide a detailed reference for identification of the tetragonal Zn3P2 phase and can be used for building Raman based methodologies for effective defect screening of bulk materials and films, which might contain structural inhomogeneities.

Lattice dynamic properties of the tetragonal modification of ZnP2 and CdP2 crystals (space group P41212, no 92) are calculated within the density functional theory. Theoretical results are shown to compare favorably with available Raman scattering and infrared reflection/transmission experimental data, which allows assignment of Raman-and infrared-active modes to the specific lattice eigenmodes. It is confirmed that several distinct features of vibrational spectra of these compounds steam from the presence of four phosphorous spiraling chains within crystallographic unit cell.

Raman scattering spectroscopy is used to monitor the transition of reduced niobium oxyfluoride ${\mathrm{Nb}}_{2}{\mathrm{O}}_{2}{\mathrm{F}}_{3}$ single crystals from their high-temperature monoclinic (I2/a) phase into the low-temperature triclinic ($P\overline{1}$) phase at ${T}_{c}\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}90\phantom{\rule{4.pt}{0ex}}\text{K}$ due to charge disproportionation of (${\mathrm{Nb}\text{\ensuremath{-}}\mathrm{Nb})}^{7+}$ dimers and creation of crystallographically nonequivalent dimers with long and short Nb-Nb bonds. The group-theoretic analysis of lattice vibrations is performed, and the assignment of observed phonon lines to the specific lattice eigenmodes of the two phases is achieved based on a comparison with the results of density functional lattice dynamics calculations. Nb-Nb dimers are found to possess stretching vibrational frequencies as high as 382 ${\mathrm{cm}}^{\ensuremath{-}1}$. Strikingly, the kinetics of the monoclinic-to-triclinic structural transformation and the volume fraction of corresponding phases below ${T}_{c}$ are shown to strongly depend upon the sample cooling rate. Fast cooling results in a ``freezing'' of the high-temperature monoclinic phase and allows us to observe a spin-ordered state below ${\mathrm{T}}_{N}\ensuremath{\approx}$ 49 K.

The transformation of the vibrational spectrum of Cu2Zn(Sn1−xGex)S4 single crystals over the entire composition range (0 ≤ x ≤ 1) is studied experimentally by low-temperature Raman scattering and photoluminescence spectroscopies, as well as theoretically in the framework of density functional theory (DFT). It is shown that unlike “classic” mixed binary II–VI and III–V compounds, which are characterized by either one- or two-mode behavior of spectra transformation upon composition variation, the vibrational modes of the quaternary semiconductor Cu2Zn(Sn1−xGex)S4 exhibit both types of behavior within the same alloy system. DFT calculations reveal that the two-mode transformation is in fact observed for the vibrational modes, which possess a very small dispersion across the Brillouin zone, that is typical for a molecular crystal. These modes are due to the “breathing” motion of sulfur within GeS4 and SnS4 tetrahedra. The effects of structural (positional) disorder of mixed crystals are analyzed based on Raman scattering as well as photoluminescence results.

A comprehensive vibrational analysis of the kesterite Cu2ZnGeS4 semiconductor (space group I) is reported, which includes experimental in-plane rotation polarized Raman scattering measurements from the (1 0 1)-single crystal facet as well as first principle lattice dynamic calculations. 17 out of the 27 expected vibrational modes of the kesterite structure are unambiguously identified. Raman scattering measurements performed under resonant excitation conditions show a pronounced enhancement of the longitudinal optical components of the polar modes. The appearance of several additional lines in the Raman spectra have been interpreted as being due to the presence of inclusions of Cu2ZnGeS4 polymorph with the P2c lattice symmetry, which differs from the kesterite by cation sublattice arrangement.

Density-functional calculations of the electronic band structure, optical properties, and lattice dynamics of kesterite CuZnGeSe semiconductor (space group ) are reported. Theoretical optical properties of the material are shown to agree quantitatively with available spectroscopic ellipsometry experimental data that allow detailed interpretation of the main spectral features around the fundamental absorption edge. A good agreement between theoretical and experimental vibrational mode frequencies is also established and the assignment of observed phonon modes to specific lattice eigenmodes is performed.

A new niobium oxyfluoride, Nb2O2F3, synthesized through the reaction of Nb, SnO, and SnF2 in Sn flux, within welded Nb containers, crystallizes in a monoclinic structure (space group: I2/a; a = 5.7048(1)Å, b = 5.1610(1)Å, c = 12.2285(2)Å, β = 95.751(1)°). It features [Nb2X10] units (X = O, F), with short (2.5739(1) Å) Nb-Nb bonds, that are linked through shared O/F vertices to form a 3D structure configurationally isotypic to ζ-Nb2O5. Nb2O2F3 undergoes a structural transition at ∼90 K to a triclinic structure (space group: P1̅; a = 5.1791(5)Å, b = 5.7043(6)Å, c = 6.8911(7)Å, α = 108.669(3)°, β = 109.922(2)°, γ = 90.332(3)°). The transition is described as a disproportionation or charge ordering of [Nb2](7+) dimers: (2[Nb2](7+) → [Nb2](6+) + [Nb2](8+)), resulting in doubly (2.5000(9) Å) and singly bonded (2.6560(9) Å) Nb2 dimers. The structural transition is accompanied by an unusual field-independent "spin-gap-like" magnetic transition.

Spectrally-selective solar absorbers are widely used in solar hot water and concentrating solar power (CSP) systems. However, their performance at high temperatures (>450 °C) is still not satisfactory due to high infrared (IR) emittance and lack of long-term thermal stability. Here, we explore yttria-stabilized zirconia (YSZ) cermet-based spectrally-selective surfaces for high-temperature solar absorber applications. The developed multilayer selective surface comprises two sunlight-absorbing W–Ni–YSZ cermet layers with different W–Ni volume fractions inside the YSZ matrix, two anti-reflection coatings (ARCs), and one tungsten IR reflection layer for reduced IR emittance and improved thermal stability, deposited on a polished stainless steel (SS) substrate. The fabricated solar absorbers are tested for their long-term thermal stability at 600 °C. We find a distinct change in the surface morphology of the solar absorbers when oxygen is highly deficient in the YSZ-ARC layers. The oxygen deficiency can be effectively overcome through increasing the oxygen partial pressure during sputtering, which leads to a stable solar absorber with a solar absorptance of ∼0.91 and a total hemispherical emittance of ∼0.13 at 500 °C. Those values are obtained at the actual operating temperature using an absolute and direct method that measures the total hemispherical emittance with high accuracy. In contrast, most reports on solar absorber development in the literature to date use only near room-temperature spectroscopy techniques that have been shown to significantly underestimate the total hemispherical emittance. This makes our experimentally demonstrated total hemispherical emittance value the lowest ever reported for a high-temperature stable solar absorber with solar absorptance above 0.9.

This work presents a comprehensive analysis of the structural and vibrational properties of the kesterite Cu

BaMn(9)[VO(4)](6)(OH)(2) was synthesized by hydrothermal methods. We evaluated the crystal structure based on the two possible space groups P2(1)3 and Pa3̅ [a = 12.8417(2) Å] using single-crystal and powder X-ray diffraction techniques. The structure contains three-dimensionally linked Mn(9) units of a chiral "paddle-wheel" type. Experimental IR and Raman spectra were analyzed in terms of fundamental vanadate and hydroxide vibrational modes. The magnetic properties were investigated, and the specific heat in applied fields was studied. The dominant magnetic interactions (Mn(2+), S = 5/2) are of antiferromagnetic origin, as indicated by a Curie-Weiss fit above 175 K with Θ ≈ -200 K. Canting of the spins on the geometrically frustrated triangle segment of the structural feature is considered to account for the ferrimagnetic type of long-range order at T(C) ≈ 18 K. We propose a model for the spin structure in the ordered regime. Dielectric constants were measured and indicate a magnetodielectric effect at T(C), which is assigned to spin-lattice coupling.

We report the results of a Raman spectroscopy study of lattice vibrations in colloidal Cu3SnS4 nanocrystals (NCs) in a broad spectral range between 70 and 1200 cm–1. The crystallographic structure ...

This work brings together diamond anvil cell techniques, vibrational spectroscopies, and complementary lattice dynamics calculations to investigate pressure-induced local lattice distortions in α-Co[N(CN)2]2. Analysis of mode behavior and displacement patterns reveals a series of pressure-driven transitions that modify the CoN6 counter-rotations, distort the octahedra, and flatten the C-N(ax)-C linkages. These local lattice distortions may be responsible for the low temperature magnetic crossover. We also discuss prospects for negative thermal expansion and show that there is not a straightforward low pressure pathway between the pink α and blue β ambient pressure phases of Co[N(CN)2]2.

We report the results of non-resonant and resonant Raman scattering in orthorhombic nanocrystalline CuInS2 semiconductor, supported by density functional first principle lattice dynamics calculations. A larger number of dominant phonon modes in comparison with standard tetragonal CuInS2 phases is shown to be associated with peculiarities of cation sublattice ordering and is the “fingerprint” of the corresponding structural polymorph. Good overall agreement is found between theoretical and experimental phonon mode frequencies.

a b s t r a c t The zone-center phonons and the frequency-dependent dielectric function of the brookite phase of TiO2 are studied experimentally by means of polarized Raman and infrared spectroscopy. The Raman- and infrared-active modes are unambiguously identified by symmetry. The mode frequencies are in good agreement with those predicted by the density function calculations of lattice dynamics.

The structures of two trigonal-rhombohedral CaSi

Single crystals of the new title compounds are hydrothermally synthesized from aqueous mixtures of NH4VO3 dissolved in concentrated NH4OH, CuX2 (X: Cl, Br), Ba(OAc)2, and LiX (autoclave, pH 8—10, 220 °C, 2—4 d, 25 and 55% yield for X: Cl and Br, resp.).

Na5[FeO3][OH] has been obtained from a redox reaction between iron metal and CdO in the presence of Na2O and NaOH at 450 °C (5 d) as red crystals. The structure has been determined from single crystal data (Pnma, Z = 8, a = 990.94(7) pm, b = 1016.41(7) pm, c = 1185.35(8) pm, wR2 = 0.050) and evaluated by MAPLE calculations. In addition, we present experimental single-crystal IR and Raman spectroscopic data to discuss aspects of the isolated [FeO3]4– complexes and non-coordinating hydroxide in comparison with the respective cobalt compounds. Additional ab-initio lattice dynamic calculations are included for comparison.

Single crystal polarized Raman and infrared spectra of the series Na(5)[MO(2)][X] with M = Co(I), Ni(I), and Cu(I) and X = S(2-) and CO(3)(2-), are reported. All phonon modes are assigned to the lattice eigenmodes based on the group theory analysis and first principles lattice dynamics calculations. The energies of the fundamental symmetric and asymmetric vibrations of the [MO(2)](3-) complex are discussed on the basis of their electronic structure and variation in M-O interatomic distances. Electronic Raman scattering and luminescence are observed for the magnetic members of the series (Co(I), d(8), and Ni(I), d(9)). Ligand field theory is employed to account for the electronic effects which originate from states split by spin-orbit coupling.

Nickel silicides are widely used as contact materials for electronic devices based on silicon (Si). However, they have been predominantly fabricated by annealing separate Ni and Si phases which leads to phase and structural complexity. In this letter, direct epitaxial growth of a single-phase nickel disilicide (NiSi2) thin film by sputter deposition of NiSi2 is achieved on low-cost and flexible Hastelloy tapes which offers a promising route to fabricate low-cost, flexible electronic devices. Biaxially textured titanium nitride (TiN) is applied as the seeding layer and the diffusion barrier under NiSi2. An epitaxial relationship of (001)⟨100⟩NiSi2 ǁ (001)⟨110⟩TiN is observed with an extra-large lattice mismatch (∼10.3%) between NiSi2 and TiN. Both the bonding similarity and the passivation effect by hydrogen promote the epitaxial growth of NiSi2 on TiN. The flat and smooth NiSi2 thin film consists of grains with a size of 50–100 nm. An epitaxially grown Si film on NiSi2 further demonstrates the potential of manufacturing high-performance Si flexible electronics with NiSi2/TiN/Hastelloy as the direct contact through this approach.

Optical and vibrational properties of a novel allotrope of elemental germanium Ge(oP32), which crystallizes in the structure corresponding to the orthorhombic space group Pbcm, are studied experimentally by means of absorption and polarized Raman scattering measurements and theoretically using the first principles density functional theory. Material is found to be a direct band gap semiconductor with E g = 0.33 eV. Out of theoretically predicted 48 Raman-active modes, 27 are observed in the spectra and assigned to the specific lattice eigenmodes of the crystal based on their symmetry and a comparison with the results of first principles lattice dynamics calculations. Remarkably, the highest frequency vibration is observed at 316 cm-1, that is higher than the cubic crystalline [Formula: see text]-Ge mode at 300 cm-1. Exceptional sharpness of observed phonon lines (between 0.8 and 2.5 cm-1 at T = 10 K) implies excellent crystallinity of Ge(oP32) crystals.