Increase In Cr3 Research Articles

Spectroscopic and luminescence studies of Cr3+ doped cadmium silicate nano-phosphor

CdSiO3:Cr3+ (1–9mol%) nanophosphor was synthesized by a low temperature solution combustion technique. The final products were well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy, transmission electron microscopy as well as Fourier transform infra-red, Raman and UV–visible spectroscopies. The PXRD results revealed that the samples were well crystallized with monoclinic phase. The average crystallite sizes estimated by Scherrer׳s method, Williamson–Hall (W–H) plots and size–strain plot were found to be in the range of 20–45nm. The energy band gap of the phosphors was found to be in the range of 5.42–5.47eV. Photoluminescence studies show an intense emission peak at 691nm for the excitation wavelength of 361nm, which corresponds to 2Eg→4A2g transition of R-line of chromium. Racah parameters were estimated to describe the effects of electron–electron repulsion within the crystal lattice. It was observed that PL intensity increases with increase in Cr3+ concentration. The highest PL intensity was observed from 7mol% doped sample and thereafter, it decreases with further increase in Cr3+ concentration; this may be due to cross relaxation leading to a concentration quenching. The chromaticity co-ordinates and correlated color temperature of all the phosphors were well located in red region, which is a high potential for the fabrication of red component of white light emiting diodes (WLEDs).

Effect of Cr3+ substitution on properties of nano-ZnFe2O4

Nano-crystalline ferrite materials with general formula ZnCrxFe2−xO4 (x=0.1, 0.2, 0.3, 0.4 and 0.5) have been synthesized by chemical co precipitation method. The developed materials were characterized for structural, shape/size and electrical properties by using analytical techniques viz. X-ray diffraction (XRD), transmission electron microscopy (TEM), and impedance analyzer respectively. X-ray diffraction pattern confirms the formation of single phase spinel structure of prepared ferrites. The lattice constant of ZnCrxFe2−xO4 (x=0.1, 0.2, 0.3, 0.4 and 0.5) nano-particles decreases with increasing Cr3+ ion content. Nano-size of synthesized ferrite particles were confirmed by electron microscopy. DC-electrical conductivity and activation energy increases with increasing Cr3+ ion content. Dielectric loss (tanδ), real part of dielectric constant (ɛ′), imaginary part of dielectric constant (ɛ″), ac conductivity (σac), real (resistive) part of impedance (Z′) and imaginary part of impedance (Z′′) were analyzed as a function of frequency, composition and temperature using impedance analyzer in the frequency range of (1KHz–5MHz) and temperature range of (300–523K). Dielectric loss (tanδ), dielectric permittivity (ɛ′) and ac conductivity (σac) decreases with increase in Cr3+ substitution which has been explained on the basis of hopping mechanism. Electrical conductivity increases with increasing temperature revealing the semiconducting behavior of prepared ferrites as also observed by the variation in cole–cole plots with temperature. The Nyquist impedance plots of the prepared ferrites clearly reveal the inherent phenomenon involved in conduction mechanism of Cr3+ substituted ZnFe2O4 ferrites.

Chemical synthesis and magnetic investigations on Cr3+ substituted Zn-ferrite superparamagnetic nano-particles

In present report, we have discussed the effect of Cr3+ substitution on structural and magnetic properties of ZnFe2−xCrxO4 (x=0, 0.1, 0.3, 0.5) ferrite nano-particles synthesized by a chemical co-precipitation method using oleic acid as surfactant. Structural studies were carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. XRD pattern of the prepared powder samples annealed at 350°C confirmed the formation of single phase cubic spinel structure. TEM images confirmed the nano size formation of particles. A Vibrating Sample Magnetometer (VSM) has been employed to probe the change in magnetic properties with change in composition. Magnetic particle size (Dm) calculated from hysteresis loop was found less than the particle size (DT) calculated from TEM micrograph due to spin canting effect. The magnetization studies inferred that magnetic moment (ηB) showed decreasing trend with increase in Cr3+ substitution, its value decreases from 0.548 (for x=0.0) to 0.125 (for x=0.5). The saturation magnetization (MS) value was found to decrease from 12.76emu/gm (for x=0.0) to 2.92emu/gm (for x=0.5). The coercivity (Hc) was found to change proportionally with the particle sizes of investigated ferrites. Squareness (S) values revealed that particles interact by magnetostatic interactions. The M–H loop of all the samples is narrow with low value of coercivity and retentivity; indicate the superparamagnetic nature of these samples.

Synthesis, structural and dielectric properties of Cr3+ substituted Fe3O4 nano-particles

FeCrxFe2−xO4 (x==0.1, 0.2, 0.3, 0.4 and 0.5) nano-particles were synthesized by a chemical co precipitation method and the effect of Cr3+ substitution on structural and dielectric properties of Fe3O4 was studied. Structural studies were carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. XRD pattern confirmed the single spinel ferrite phase formation. Particle size and crystallite size of the synthesized materials lie in the range of 25–50nm as calculated from electron microscopy images and X-ray diffraction patterns using Scherrer׳s formula. Dielectric loss (tanδ), real part of dielectric constant (ε′), imaginary part of dielectric constant (ε″), ac conductivity (σac), real (resistive) part of impedance (Z′) and imaginary part of impedance (Z″) were evaluated as a function of frequency, composition and temperature using an impedance analyzer in the frequency range of (1kHz–5MHz) and temperature range of (27–250°C). AC conductivity (σac) was found to decrease with increase in Cr3+ ion doping and can be explained on the basis of hopping mechanism. The variation of dielectric loss (tanδ), dielectric permittivity (ε′), ac conductivity (σac) with temperature and frequency can be explained on the basis of Maxwell–Wagner type of interfacial polarization and hopping mechanism between ferrous and ferric ions at octahedral site. Variation in Cole–Cole plots with temperature shows decrease in resistivity with increase in temperature. The Nyquist impedance plots of the prepared materials reveals the inherent phenomenon involved in conduction mechanism of Cr3+ substituted Fe3O4 ferrites. Behavior of DC electrical resistivity with increasing temperature indicates that the substituted ferrites have semiconductor like behavior. Activation energy was found to increase with increasing Cr3+ ion content.

Synthesis, characterization and spectroscopic investigation of Cr3+ doped wollastonite nanophosphor

This work explores the preparation of nanocrystalline Cr3+ (1–5mol%) doped CaSiO3 phosphors by solution combustion process and study of its photoluminescence (PL) behavior. The nanopowders are well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra-red (FTIR) spectroscopy. PXRD results confirm monoclinic phase upon calcination at 950°C for 3h. SEM micrographs indicates that the powder is highly porous and agglomerated. The TEM images show the powder to consist of spherical shaped particles of size ∼30–60nm. Upon 323nm excitation, the emission profile of CaSiO3:Cr3+ exhibits a narrow red emission peak at 641nm due to 2E→4A2transition and broad band at 722nm due to 4T2g→4A2g. It is observed that PL intensity increases with increase in Cr3+ concentration and highest PL intensity is observed for 3mol% doped sample. The PL intensity decreases with further increase in Cr3+ doping. This decrease in PL intensity beyond 3mol% is ascribed to concentration quenching. Racah parameters are calculated to describe the effects of electron–electron repulsion within the crystal lattice. The parameters show 21% reduction in the Racah parameter of free ion and the complex, indicating the moderate nephelauxetic effect in the lattice.

Structural development and magnetic phenomenon in Zn–Cr–Fe multi oxide nano-crystals

The Cr3+ ions doped multi-oxide ZnFe2−xCrxO4 ferrite nanoparticles have been synthesized by chemical co-precipitation method. Site occupancies of Zn2+, Cr3+ and Fe3+ ions were analyzed using X-ray diffraction data and Buerger's method. The effect of the constituent phase variation on the magnetic hysteresis behavior was examined by saturation magnetization which decreases with the increase in Cr3+ content in place of Fe3+ ions at octahedral B-site. Typical blocking temperature (TB) around 90K was observed by zero field cooling and field cooling magnetization study. Room temperature Mössbauer spectra show two paramagnetic doublets (tetrahedral and octahedral sites). The isomer shifts of both doublets decrease whereas quadrupole splitting and relative area of tetrahedral A-site increases with increasing Cr3+ substitution. The dielectric constant (measured on compositions x=0, 0.4, 0.8 and 1.0) increases when the temperature increases as in the semiconductor. This behavior is attributed to the hopping of electrons between Fe2+ and Fe3+ ions with a thermal activation.

Magnetic Hysteresis and Complex Initial Permeability of Cr<sup>3+</sup> Substituted Mn-Zn Ferrites

The impact of Cr3+ ion on the magnetic properties of Mn0.50Zn0.50CrxFe2-xO4 (with x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) has been studied. Ferrite samples were synthesized by combustion method and sintered at various temperatures (1250°C, 1300°C and 1350°C). The structural properties were investigated by means of X-ray diffraction patterns and indicated that the samples possess single phase cubic spinel structure. The lattice parameter decreases with the increase in Cr3+ content, as the ionic radius of Cr3+ ion is smaller than that of Fe3+. The average grain size (D), bulk density (ρB) and initial permeability （μi’ ）decreases with increase in Cr3+ content whereas porosity follows its opposite trend. The ρB was found to increase with increase in Cr3+ content as the sintering temperature (Ts) is increased from 1250°C to 1350°C. The Ts affects the densification, grain growth and （μi’ ） of the samples. The （μi’ ） strongly depends on average grain size, density and intragranular porosity. The B-H loops of the compositions were measured at room temperature. The saturation magnetization (Ms), coercivity (Hc) and hysteresis losses were studied as a function of Cr3+ content. The Ms was found to decrease with the increase of Cr3+ content, which is attributed to the dilution of A-B interaction.

Adsorption of Cr(III) from acidic solutions by crop straw derived biochars

Cr(III) adsorption by biochars generated from peanut, soybean, canola and rice straws is investigated with batch methods. Adsorption of Cr(III) increased as pH rose from 2.5 to 5.0. Adsorption of Cr(III) led to peak position shifts in the FTIR-PAS spectra of the biochars and made zeta potential values less negative, suggesting the formation of surface complexes between Cr3+ and functional groups on the biochars. The adsorption capacity of Cr(III) followed the order: peanut straw char > soybean straw char > canola straw char > rice straw char, which was consistent with the content of acidic functional groups on the biochars. The increase in Cr3+ hydrolysis as the pH rose was one of the main reasons for the increased adsorption of Cr(III) by the biochars at higher pH values. Cr(III) can be adsorbed by the biochars through electrostatic attraction between negative surfaces and Cr3+, but the relative contribution of electrostatic adsorption was less than 5%. Therefore, Cr(III) was mainly adsorbed by the biochars through specific adsorption. The Langumir and Freundlich equations fitted the adsorption isotherms well and can therefore be used to describe the adsorption behavior of Cr(III) by the crop straw biochars. The crop straw biochars have great adsorption capacities for Cr(III) under acidic conditions and can be used as adsorbents to remove Cr(III) from acidic wastewaters.

Magnetic properties of Cr-substituted Co-ferrite nanoparticles synthesized by citrate-gel autocombustion method

Abstract A series of Co-Cr nanoferrites having the chemical formula CoCr x Fe2 − x O4 (x = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0) were synthesized by citrate-gel autocombustion method at a very low temperature (180°C). The X-ray diffraction analysis of as-synthesized powders and sintered powders has confirmed the formation of single-phase cubic spinel structure. The average particle size of the synthesized ferrites was 6 to 12 nm. Magnetic susceptibility measurements using Faraday magnetic susceptibility balance showed the paramagnetic nature of the ferrites. Magnetic properties of Co-Cr nanoferrites were measured using a vibrating sample magnetometer at room temperature in the applied field of 15 kOe. The saturation magnetization decreased from 33.84 to 13.83 emu/g with increase in Cr3+ concentrations, indicating the fact that the lesser magnetic Cr3+ ions substitute Fe3+ ions in the octahedral sublattice of the ferrite. With improvement in the magnetic properties, the synthesized nanoferrites become soft magnetic materials. Such materials are useful in transformer and motor cores to minimize the energy dissipation with the alternating fields associated with AC electrical applications. The coercivity of pure CoFe2O4 was larger than that of the Cr-doped cobalt ferrites.

Influence of chromium ion substitution on the structure and properties of zinc ferrite synthesized by the sol–gel auto-combustion method

Nanocrystalline powders of chromium substituted zinc ferrites with the general formula ZnFe2−xCrxO4 (0⩽x⩽2) were obtained by the sol–gel auto-combustion method, using tartaric acid as a combustion-complexing agent. The solid phase chemical reactions were monitored using infrared spectroscopy, finally indicating the absence of organic phases. The XRD results confirmed the spinel mono-phase formation in the 24–36nm crystallite size range. Nanosized particle formation was confirmed through scanning electron microscopy. The cation distribution in the samples was estimated theoretically and the results showed that all the compounds had a mixed ionic distribution. The magnetic properties of the samples were studied using a vibrating sample magnetometer and showed that the increase in Cr3+ concentration in the Zn ferrite caused a reduction in the hysteresis losses and a non-linear reduction in the saturation magnetization. The electrical analysis showed very low values of dielectric loss at frequencies over 1MHz.

Doping effect of Cr3+ ions on the structural, magnetic and electrical properties of Co–Cd ferrites: A study on the redistribution of cations in CoCd0.4CrxFe1.6−xO4 (0.1 ≤ x ≤ 0.6) ferrites

Increasing chromium substitution in Co–Cd ferrites, synthesized via sol–gel auto-combustion method, remarkably influences their structural, magnetic and electrical properties. As the Cr3+ concentration is increased, various interesting changes in the values of structural parameters like X-ray density, bulk density and porosity have been observed. The value of lattice constant, is found to be ∼8.38 Å with an average crystallite size of ∼50 nm. The porosity in the entire ferrite samples is low (5.3%–6.9%). The magnetic properties, like saturation magnetization and coercivity, show a decrease trend with increase in Cr3+ concentration. The proposed cation distribution is further substantiated by the electrical properties. It is observed that the d.c. resistivity increases with Cr3+ concentration, suggesting occupancy of Cr3+ ions in the B-sites which leads to the dilution of Fe2+–Fe3+ conduction. The activation energy calculated from the d.c. resistivity vs temperature curves is found to be ∼0.25 eV.

Effect of Cr Substitution on Magnetic Properties of Mg Nanoferrites Synthesized by Citrate‐Gel Auto Combustion Method

A series of Mg‐Cr nanoferrites with the chemical formula MgCrxFe2−xO4 (0.0 ≤ x ≤ 1.0) were synthesized by Citrate‐Gel auto combustion method. The formation of single phase cubic spinel structure of the samples was confirmed by X‐ray diffraction (XRD) analysis. It is observed that with the increase in the paramagnetic Cr content, the particle size of the ferrite compositions has decreased from 23 nm to 7 nm. Faraday magnetic Susceptibility Balance was used to measure the Magnetic susceptibility of synthesized samples that confirmed the paramagnetic nature of the ferrites. Vibrating Sample Magnetometer (VSM) was used to measure the Magnetic properties of nanoferrites under investigation at room temperature under the applied magnetic field of 15 kOe. With the increase in Cr3+ concentration, the saturation magnetization has decreased from 11 emu/g to 1.5 emu/g.

Influence of Cr3+ substitution on the electrical and magnetic properties of Ni0.4Cu0.4Zn0.2Fe2O4 nanoparticles

AbstractThe Ni0.4Cu0.2Zn0.4ferrites with different concentrations of Cr3+were synthesized at a low temperature (450°C) using sol–gel auto-combustion method. The X-ray diffraction analysis of the samples confirms the formation of a single-phase cubic spinel structure. The lattice constant decreases from 8.331 to 8.253 Å with an increase in Cr3+substitution. Bulk density decreases from 4.95 to 4.71 gm/cm3whereas porosity increases from 9.34% to 14.76% with an increase in Cr3+substitution. Transmission electron microscopy was adopted to determine the particle size. Particle size decreases from 19 to 13 nm with the addition of Cr3+ions. Saturation magnetization, coercivity, and other hysteresis parameters were measured using a vibrating sample magnetometer at room temperature with a maximum magnetic field of 8 kOe. Magnetization decreases from 62 to 48 emu/g, whereas coercivity increases from 65 to 180 Oe. The direct current (DC) resistivity increases from 3.62 × 106to 4.21 × 106Ω cm with Cr3+contentx. The dielectric constant (ε′) decreases with increasing concentration of Cr3+ions.

Fabrication of Co0.5Ni0.5CrxFe2−xO4 materials via sol–gel method and their characterizations

Co0.5Ni0.5CrxFe2−xO4 nanoparticles have been designed by the sol–gel auto combustion method, using nitrates of the respective metal ions, and citric acid as the starting materials. The process takes only a few minutes to obtain as-received Cr-substituted Co–Ni ferrite powders. X-ray diffraction (XRD), vibrational sample magnetometer (VSM), transmission electron microscopy (TEM) are utilized in order to study the effect of variation in the Cr3+ substitution and its impact on particle size, lattice constant, specific surface area, cation distribution and magnetic properties. Lattice parameter, particle size found to decrease with increasing Cr3+ content, whereas specific surface area showed increasing trend with the Cr3+ substitution. Cation distribution indicates that the Cr, Co and Ni ions show preference toward octahedral [B] site, whereas Fe occupies both tetrahedral (A) and octahedral [B] sites. Saturation magnetization (MS) decreased from 65.1 to 40.6emu/g with the increase in Cr3+ substitution. However, Coercivity increased from 198 to 365Oe with the Cr3+ substitution.

Infrared spectral and elastic moduli study of NiFe2−xCrxO4 nanocrystalline ferrites

Nanocrystalline ferrites with general formula NiFe2−xCrxO4 (x=0.0−1.0) were prepared by the wet chemical method. Infrared spectra were scanned in the range of 300–800cm−1. Three absorption bands were observed in the infrared spectra, the high frequency band ν1 is assigned to tetrahedral complex, low frequency band ν2 to octahedral complex and a small band ν3 is due to Fe3+O2− complex. The force constant, bond length, and the Debye temperature was determined by infrared spectra analysis. The force constant and bond length decrease with the increase in Cr3+ content x which suggests the weakening of the inter atomic bonding. The force constant, lattice constant, and pore fraction have been used to calculate elastic moduli such as stiffness constant, Young's modulus, bulk modulus, rigidity modulus, Poisson's ratio, wave velocity and the Debye temperature. The values of elastic moduli and the Debye temperature decrease with the increase in Cr3+ content x whereas Poisson's ratio almost remains constant. Results have been explained on the basis of inter atomic bonding.

Enhancement of electrical properties due to Cr3+ substitution in Co-ferrite nanoparticles synthesized by two chemical techniques

Nanocrystalline cobalt ferrites with nominal composition CoCrxFe2−xO4 ranging from x=0.0 to 0.5 with step increment of 0.25 were prepared by sol–gel auto combustion and chemical co-precipitation techniques. A comparative study of structural, electrical and magnetic properties of these ferrites has been measured using different characterization techniques. Structural and micro-structural studies were measured using X-ray diffraction, Fourier transform infra-red spectroscopy (FTIR), scanning electron microscopy and atomic force microscopy. Crystallite sizes of the series are within the range of 12–29±2nm. Lattice parameters decrease by increasing Cr3+ concentration. FTIR confirms the presence of two lattice absorption bands. DC electrical resistivity increases to a value of ∼1010Ω-cm with increase in Cr3+ concentration, but the most significant increase is in samples prepared by sol–gel combustion. Dielectric properties have been measured as a function of frequency at room temperature. Dielectric loss decreases to 0.1037 and 0.0108 at 5MHz for chemical co-precipitation and sol–gel combustion, respectively. Impedance measurements further helped in analyzing the electrical properties and to separate the grain and grain boundary resistance effects using a complex impedance analysis. Magnetic parameters were studied using a vibrating sample magnetometer in the applied field of 10kOe. The saturation magnetization decreased from 63 to 10.8emu/gm with increase in Cr3+ concentration.

Investigation of structural, magnetic, electrical and optical properties of chromium substituted cobalt ferrites (CoCrxFe2−xO4, 0⩽x⩽1) synthesized using sol gel auto combustion method

The structural, magnetic, electrical and optical properties of chromium substituted cobalt ferrites (CoCrxFe2−xO4, x = 0.2, 0.4, 0.6, 0.8 and 1.0), have been investigated and on the basis of the saturation magnetization values, the cation distribution in the ferrite samples has been proposed. It is suggested that both Co2+ ions as well as Cr3+ ions seek to the octahedral sites of the ferrite sub-lattice. However, a small amount of Co2+ ions are also incorporated in the tetrahedral sites of the ferrite sub-lattice. This causes a decrease in the saturation magnetization (Ms) values with increasing Cr3+ concentration. The increase in Cr3+ ion composition in the ferrite sample decreases the value of saturation magnetization from 77 emu/g to 13 emu/g, indicative of the fact that the lesser magnetic Cr3+ ions substitute Fe3+ ions in the octahedral sub-lattice of the ferrites. A significant decrease in the saturation magnetization is observed in CoCrFeO4, attributing to the weakening of the A–B interaction as iron enters into the A site. The magnetic moments calculated from the proposed cation distribution (using Neel’s two sub-lattice model) are in conformity with those obtained from Ms values. The effect of annealing temperature on structural, magnetic, electrical and optical properties has also been investigated.

Frequency and temperature dependent electrical properties of Ni0.7Zn0.3CrxFe2−xO4 (0 ≤ x ≤ 0.5)

Series of the ferrite samples with a chemical formula Ni0.7Zn0.3CrxFe2−xO4 (x=0.0–0.5) were prepared by a sol–gel auto-combustion method and annealed at 600°C for 4h. The prepared samples have the cubic spinel structure with no impurity phase. As the Cr3+ content x increases, the unit cell dimensions decrease with an increase in Cr3+ content x. The crystallite size is decreases from 37nm to 21nm as the Cr3+ content increases from x=0.0 to 0.5. Resistivity increases whereas dielectric constant decreases with an increase in Cr3+ content x. Maxima in the dielectric loss tangent versus frequency appear when the frequency of the hopping charge carriers coincides with the frequency of the applied alternating field. Dielectric constant and dielectric loss tangent increases with increase in temperature. Saturation magnetization of sintered samples showed higher values as compared to as-prepared sample. Curie temperature deduced from AC susceptibility data decreases with increasing x.

Cation distribution study of nanocrystalline NiFe2−xCrxO4ferrite by XRD, magnetization and Mössbauer spectroscopy

AbstractThe spinel ferrite systems NiFe2−xCrxO4(withx = 0.0–1.0 in step of 0.2) were prepared by wet chemical co‐precipitation method, using sulphates of respective metal ions. Formation of single phase spinel crystal structure of sample has been confirmed by X‐ray diffraction method. Magnetic parameters such as coercivity and saturation magnetization are measured by employing vibrating samples magnetometer (VSM). The saturation magnetization and magneton number (nB) decreases with increase in Cr3+contentx. The Mössbauer spectra taken at 300 K and spectra are assigned to two strongly overlapping sextets corresponding to tetrahedral A sites and octahedral B sites. The cation distribution of ferrites system has been calculated by X‐ray method, the behaviour of magnetization curve and Mössbauer spectra. The evaluation of cation distribution indicates that, in Cr‐dominant region, few nickel ions occupies tetrahedral A sites which convert perfect inverse spinel to partially normal spinel structure.

Structure and optical properties of pulsed sputter deposited CrxOy∕Cr∕Cr2O3 solar selective coatings

Spectrally selective CrxOy∕Cr∕Cr2O3 multilayer absorber coatings were deposited on copper (Cu) substrates using a pulsed sputtering system. The Cr targets were sputtered using asymmetric bipolar-pulsed dc generators in Ar+O2 and Ar plasmas to deposit a CrxOy (bottomlayer)∕Cr∕Cr2O3 (top layer) coating. The compositions and thicknesses of the individual component layers have been optimized to achieve high absorptance (0.899–0.912) and low emittance (0.05–0.06). The x-ray diffraction data in thin film mode showed that the CrxOy∕Cr∕Cr2O3 coating consists of an amorphous phase; the Raman data of the coating, however, showed the presence of A1g and Eg modes, characteristic of Cr2O3. The x-ray photoelectron spectroscopy (XPS) data from near-surface region of the absorber suggested that the chemical state of Cr was in the form of Cr3+ and no phases of CrO2 and CrO3 were present. The experimental spectroscopic ellipsometric data have been fitted with theoretical models to derive the dispersion of the optical constants (n and k). The optical constants of the three layers indicate that the bottom two layers are the main absorber layers and the top Cr2O3 layer, which has higher oxygen content, acts as an antireflection coating. In order to study the thermal stability of the CrxOy∕Cr∕Cr2O3 coatings, they were subjected to heat treatment (in air and vacuum) at different temperatures and durations. The coating deposited on Cu substrates exhibited high solar selectivity (α∕ε) of 0.895∕0.06 even after heat treatment in air up to 300°C for 2h. At higher temperatures, the solar selectivity decreased significantly (e.g., α∕ε=0.855∕0.24 at 350°C in air), which is attributed to oxidation of Cr crystallites, increased surface roughness, and formation of CuO. The formation of CuO and the increase in Cr3+ vacancies due to the outward diffusion of Cr at higher annealing temperatures were confirmed by XPS. In the case of vacuum annealing, for temperatures greater than 500°C the outward diffusion of Cu was the dominating degradation mechanism. The microstructural stability of the absorber coatings heat treated in air (up to 325°C) and vacuum (up to 600°C) was confirmed by micro-Raman spectroscopy measurements. Studies on the accelerated aging tests indicated that the absorber coatings on Cu were stable in air up to 250h at 250°C with a solar selectivity of 0.898∕0.11.