Infrared Reflectance Spectra Research Articles

Multiferroic properties of Gd/Er doped chromium ferrite nano sized particles synthesized by citrate auto combustion method

The non-stoichiometric Gd/Er doped Chromium nano ferrite with uniform and tunable size has been successfully synthesized by citrate auto combustion method. The prepared samples exhibit a combination of nonstoichiometry and non electroneutrality. The neutrality in the investigated samples is well maintained via the reduction of oxygen or removal of Cr ions. The ferromagnetic as well as the ferroelectric hysteresis loops of the investigated samples were studied. The obtained data shows that the antiferromagnetic nature in CrFe2O4 (CrFeO3) is turned into weak ferromagnetism in rare earth doped chromium. The substitution of rare earth ions for Fe can dramatically improve the saturation magnetization and remnant magnetization. The band gap energy was calculated from near infrared (NIR) and visible (VIS) reflectance spectra using the Kubelka-Munk function. Special attention should be given to chromium ferrite nanoparticles which are suitable candidates to be used in many applications like non-volatile data storage and camera flashes due to their ferroelectrics properties.

Cool coatings with high near infrared transmittance for coil coated aluminium

The temperature of a surface that is exposed to sunlight is influenced by the solar reflectance and the infrared emittance of the surface. A coating that reduces the surface temperature is often referred to as a cool coating. Cool coatings on building surfaces have several potential benefits, such as reduction of energy needed for cooling, improved thermal comfort, and mitigation of the urban heat island effect.In addition to low weight, aluminium is a metal that is known for its excellent reflectance properties. Recycled aluminium is now increasingly requested by the building market, both due to reduced cost as well as for environmental considerations. For building applications, surface treatments and coatings that completely hide the aluminium substrate are needed in order to obtain an attractive appearance, good corrosion properties and overall protection against outdoor environments.We see a need for a low-cost approach that can be used to obtain a cool coating on aluminium sheet. For this we have developed several different one-layer coating systems that can be applied in a coil-coating process. A total of 8 different coloured pigments with low absorption in the near infrared have been investigated with the goal to make cool coatings with various desirable colours. The coated surfaces achieved high solar reflectance by utilizing the excellent reflectance properties of the aluminium substrate. Good hiding of the substrate in the visible range and high infrared emittance has also been obtained. The colours include black and different shades of red, orange and yellow. Solar reflectance spectra and infrared reflectance spectra have been measured. From these spectra, optical properties of the coated surface such as total solar reflectance (TSR), infrared emittance and solar reflectance index (SRI) have been calculated. In addition, we also present results from weathering testing of the coated materials. The results show that the one-layer approach can be used to obtain cool coatings with high near infrared transmittance that are feasible to apply in a coil coating process.

Enhancement of the cation order and the microwave dielectric properties of Li2ZnTi3O8 through composition modulation

A series of Li2ZnTi3-xO8 ceramics (0.04 ≤ x ≤ 0.16) were prepared by the conventional solid-state ceramic route. An obvious improvement in the order degree for the Li+ and Ti4+ ions in octahedral sites was achieved by deliberately introducing a slight Ti4+ non-stoichiometry. SAED, HRTEM, and Raman analysis confirmed a well-ordered B-site structure. Correspondingly, an obvious enhancement of the quality factor up to 108,000 GHz was demonstrated for Ti-deficient Li2ZnTi2.92O8 ceramics, a 50% increase compared to the stoichiometric counterpart. Moreover, the infrared reflectivity spectrum of the Li2ZnTi2.92O8 ceramic was used to disclose the intrinsic dielectric responses of a Li-based spinel for the first time. These results provide useful insights into the structure-property relation in the spinel material system.

Crystal structure, infrared reflectivity spectra and microwave dielectric properties of CaAl2O4 ceramics with low permittivity

CaAl2O4 ceramics with low permittivity have been prepared via a solid state ceramic route. X-ray diffraction analysis and Rietveld refinement result demonstrated that CaAl2O4 ceramics belonged to the monoclinic structure with P21/n space group. Dense ceramics with homogeneous microstructures were obtained when sintered at around 1450 °C, wherein excellent microwave dielectric properties (εr = 8.9, Qf = 91,350 GHz, τf = −55 ppm/°C) were achieved as well. Moreover, the infrared reflectivity spectra were measured and fitted to understand their intrinsic dielectric properties. Considering the merits of easy preparation, cheap raw materials and most importantly, the outstanding microwave dielectric properties, CaAl2O4 ceramics are expected to be promising candidates for low loss microwave dielectric ceramics.

Structure, microwave dielectric properties, and infrared reflectivity spectrum of olivine type Ca2GeO4 ceramic

Ca2GeO4 dielectric ceramic was prepared using the conventional solid-state reaction method. Sintering behavior, crystal structure, microstructure, and microwave dielectric properties were analyzed by XRD, SEM, Raman, and Infrared reflectivity spectrum. Ca2GeO4 was found to crystallize in the olivine structure with a space group of Pnma. A dense and high-performance microwave dielectric property with permittivity ˜ 6.76 ± 0.02, Q×f value ˜ 82,400 ± 1800 GHz, and temperature coefficient ˜ -67 ± 3.4 ppm/°C were obtained in the sample sintered at 1420 °C. Infrared spectral analysis supported that the dielectric contribution for Ca2GeO4 at microwave region is dominated by absorption of phonons and there is no contribution from dipolar or other polarization mechanisms. The large negative τf values could be compensated by forming composite ceramics with CaTiO3. A low-εr of 9.02 ± 0.03, a high Q×f of 49,880 ± 1400 GHz, and a near-zero τf value of +4 ± 0.6 ppm/°C were obtained for 0.92Ca2GeO4-0.08CaTiO3 ceramic at 1420 °C for 4 h. This ceramic could be a good candidate for microwave substrate materials.

Study on Ti content in Low thermal expansion silica glass based on IR reflectance spectra

Ultra-Low thermal expansion (ULE) silica glass with essentially zero coefficient of thermal expansion is one of the most promising achievements in glass technology in a few decades. The property of the low thermal expansion coefficient makes it a suitable candidate for optical systems to be used in critical environments like space or vacuum. In this paper, by the help of ICP-OES and Infrared reflectance spectra, we measured titanium content of different samples and its corresponding reflection spectrum. We compared the linear fitting relation of Ti content with reflectivity and of Ti content with integration area of Gaussian fitting peak with a weighted average wave centre in 923cm-1. Results show that the latter one has a better correlation coefficient. By the tests of the IR reflectance spectrum of samples, we can deduce the Ti content using the linear fitting result.

Photoluminescence, conductivity and structural study of terbium doped ZnO films grown on different substrates

The effect of substrate material (Si, SiO2, Al2O3) on structural, optical and electrical properties of terbium doped ZnO films (Tb-ZnO) has been investigated by the X-ray diffraction, Raman scattering, atomic force microscopy, photoluminescence and infrared reflection methods. All films consist of micron size clusters of closely packed ZnO grains separated by deep trenches. The width of the trenches depends on the substrate material, being the largest in the Tb-ZnO/Al2O3 one. It is shown that the film on Al2O3 substrate contains the largest amount of extended and point defects. This film also demonstrates the highest intensity of Tb3+-related photoluminescence, while the film on Si substrate shows the lowest. On the contrary, the largest free carrier concentration evaluated from the infrared reflection spectra is found for Tb-ZnO/Si film and the lowest one is for the Tb-ZnO/Al2O3 film.

A low-cost and open-source platform for automated imaging

BackgroundRemote monitoring of plants using hyperspectral imaging has become an important tool for the study of plant growth, development, and physiology. Many applications are oriented towards use in field environments to enable non-destructive analysis of crop responses due to factors such as drought, nutrient deficiency, and disease, e.g., using tram, drone, or airplane mounted instruments. The field setting introduces a wide range of uncontrolled environmental variables that make validation and interpretation of spectral responses challenging, and as such lab- and greenhouse-deployed systems for plant studies and phenotyping are of increasing interest. In this study, we have designed and developed an open-source, hyperspectral reflectance-based imaging system for lab-based plant experiments: the HyperScanner. The reliability and accuracy of HyperScanner were validated using drought and salt stress experiments with Arabidopsis thaliana.ResultsA robust, scalable, and reliable system was created. The system was built using open-sourced parts, and all custom parts, operational methods, and data have been made publicly available in order to maintain the open-source aim of HyperScanner. The gathered reflectance images showed changes in narrowband red and infrared reflectance spectra for each of the stress tests that was evident prior to other visual physiological responses and exhibited congruence with measurements using full-range contact spectrometers.ConclusionsHyperScanner offers the potential for reliable and inexpensive laboratory hyperspectral imaging systems. HyperScanner was able to quickly collect accurate reflectance curves on a variety of plant stress experiments. The resulting images showed spectral differences in plants shortly after application of a treatment but before visual manifestation. HyperScanner increases the capacity for spectroscopic and imaging-based analytical tools by providing more access to hyperspectral analyses in the laboratory setting.

NdNb1-x(Mg1/4W3/4)xO4 (0.02≤x≤0.06) solid solution characterized by infrared spectrum and complex chemical theory

The dependence of the bond characters and crystal structure on microwave dielectric properties of NdNb1-x (Mg1/4W3/4)xO4 (x = 0.02–0.06) solid solution ceramics is investigated. X-ray diffraction and Rietveld refinement analysis both indicate a formation of single monoclinic phase in the whole range. Based on complex chemical bond theory, theoretical dielectric constant of the complex crystal is slightly lower than observed one, which is consistent with the analysis of infrared reflectivity spectra. The Q × f (quality factor) values are associated with the total lattice energy and average grain size. Increment of Nb-site bond energy generates a more stable structure, which makes τf (temperature coefficient of resonant frequency) continuously move towards zero. Besides, far-infrared reflectivity spectra illustrates that low-frequency modes play primary role of intrinsic dielectric properties. Excellent microwave dielectric properties and an optimal combination are: εr = 19.59, Q × f = 50339 GHz, τf = −39.62 ppm/°C at x = 0.04.

Raman spectroscopic, infrared spectra and microwave dielectric properties in the (ZrTi)1−x(Al1/2Nb1/2)2xO4 ceramics

A series of (ZrTi)1−x(Al1/2Nb1/2)2xO4 (0.12 ≤ x ≤ 0.30) ceramics with suitable sintering aids of 0.5 wt% CuO were successfully synthesized by the conventional solid-state processing. The XRD analysis suggested that the main crystalline phase of the well-densified ceramics belonged to α-PbO2-type structure. The SEM demonstrated that the appropriate sintering aids and the proper sintering temperature led to a densification of the ceramics by observing the microstructure. Raman spectroscopic and Far Infrared reflectivity spectra were applied to explore the relation between microwave dielectric properties and microstructure by learning the phonon vibrational modes. An excellent microwave dielectric properties (er ~ 36.5, Qf ~ 36200 GHz, τf ~ 0 ppm/°C) was achieved in (ZrTi)1−x(Al1/2Nb1/2)2xO4 ceramics sintered at 1350 °C for 4 h when x = 0.18. The results revealed this ceramic system is a very promising candidate for microwave dielectric applications requiring extremely near zero τf.

Mineral footprints of the Paleoproterozoic sediment-hosted Abra Pb-Zn-Cu-Au deposit Capricorn Orogen, Western Australia

The minerals exploration undercover relies on the understanding of the ore-forming processes and the associated alteration characteristics that are used in vectoring towards a deposit. Previously, the proposed process for forming the 1590 Ma Abra base-metal deposit, hosted at 250 m depth in the Paleoproterozoic Edmund Basin of the Western Australian Capricorn Orogen, was through exhalation to the seafloor (SEDEX-style). Lacking any visible signs of alteration, sediments overlying the Abra deposit were perceived as younger, unaltered, and cutting the mineralisation and associated alteration comprised of siderite, chlorite and minor sericite. However, a recent study delineated a phengitic (i.e. Al-poor, Mg-, Fe-, Si-rich) white mica footprint in regolith above the deposit from hyperspectral field and remote sensing data. This study links the surficial mineral footprint to the deposit below through detailed analysis of hyperspectral data from drill core. The hyperspectral data processing results were validated using optical microscopy, micro-XRF and SEM-EDS analysis, and compared with geochemical, lithological and structural drill core data. Hyperspectral short-wave infrared (SWIR) data revealed a vertically zoned alteration footprint from the deposit to the surface, where very fine-crystalline phengitic white mica (i.e. sericite) and chlorite are most abundant a few tens of metres above the deposit. The abundance of chlorite gradually decreases, and the distal phengitic alteration is cut by the present erosional surface, but only moderately affected by weathering, confirming the surficial footprint detected in the previous study. Similarly, a vertically zoned carbonate alteration was delineated from thermal infrared (TIR) reflectance spectra from drill cores up to 2 km away from the deposit. Carbonate alteration from proximal to distal comprised of Mn-rich siderite, ankerite and ferroan dolomite, which replace the dolomite matrix in coarse-grained stratigraphic sequences. The replacement of dolomite matrix suggests that these permeable horizons acted as fluid conduits, which channelled hydrothermal fluids into sedimentary strata from a feeder structure. The presence of a vertically zoned carbonate and chlorite-phengite footprint in the overlying sediments advocates for their deposition before the ore formation at Abra, and a sub-seafloor replacement within a permeable sedimentary sequence as the ore-forming process. Comparable alteration footprints have been described around some world-class sediment-hosted base-metal deposits, including the Sullivan in the British Columbia, which is considered as a classic SEDEX-style by some and an exhalative-replacement hybrid by others. Also, identical footprints are common around the volcanic-hosted massive sulphide and are associated with the carbonate replacement-style deposits – an overlap which is an interesting future research space where hyperspectral technologies could provide answers. Validated hyperspectral data combined with geochemical, lithological and structural information enabled the identification of a subtle mineral footprint above the Abra deposit, and the established method can be used for vectoring towards other buried mineralisations – even through weathering.

Ongoing resurfacing of KBO Eris by volatile transport in local, collisional, sublimation atmosphere regime

Kuiper belt object (KBO) Eris is exceptionally bright with a greater visible geometric albedo than any other known KBO. Its infrared reflectance spectrum is dominated by methane, which should form tholins that darken the surface on timescales much shorter than the age of the Solar System. Thus one or more ongoing processes probably maintain its brightness. Eris is predicted to have a primarily nitrogen atmosphere that is in vapor pressure equilibrium with nitrogen-ice and is collisional (not ballistic). Eris’s eccentric orbit is expected to result in two atmospheric regimes: (1) a period near perihelion when the atmosphere is global (analogous to the atmospheres of Mars, Triton, and Pluto) and (2) a period near aphelion when only a local atmosphere exists near the warmest region (analogous to the atmosphere of Io). A numerical model developed to simulate Eris’s thermal and volatile evolution in the local atmosphere regime is presented. The model conserves energy, mass, and momentum while maintaining vapor pressure equilibrium. It is adaptable to other local, collisional, sublimation atmospheres, which in addition to Io and Eris, may occur on several volatile-bearing KBOs. The model was applied for a limiting case where Eris is fixed at aphelion and has an initial nitrogen-ice mass everywhere equal to the precipitable column of nitrogen in Pluto's atmosphere during the New Horizons encounter (the resultant mass if the Pluto atmosphere collapsed uniformly onto the surface). The model results indicate that (1) transport of nitrogen in the local, collisional, sublimation atmosphere regime is significant, (2) changes of Eris’s albedo or color from nitrogen transport may be observable, and (3) uniform collapse of a global, nitrogen atmosphere likely cannot explain Eris’s anomalous albedo in the present epoch. Seasonal volatile transport remains a plausible hypothesis to explain Eris’s anomalous albedo and geologic processes that renew Pluto’s brightest surfaces, such as convection and glaciation, may also be operating on Eris.

Discrimination of liana and tree leaves from a Neotropical Dry Forest using visible-near infrared and longwave infrared reflectance spectra

Increases in liana abundance in tropical forests are pervasive threats to the current and future forest carbon stocks. Never before has the need been more evident for new approaches to detect the presence of liana in ecosystems, given their significance as fingerprints of global environmental change. In this study, we explore the use of longwave infrared reflectance (LWIR, 8–11 μm) as a wavelength region for the classification of liana and tree leaves and compare classification results with those obtained using visible-near infrared reflectance data (VIS-NIR, 0.45–0.95 μm). Twenty sun leaves were collected from each of 14 liana species and 21 tree species located at the canopy or forest edge (n = 700) in Santa Rosa National Park, Costa Rica. LWIR and VIS-NIR reflectance measurements were performed on these leaves using a portable calibrated Fourier Transform Infrared Spectroscopy (FTIR) Agilent ExoScan 4100 and a UniSpec spectral analysis system, respectively. The VIS-NIR and LWIR data were first resampled. Then these two spectral libraries were pre-processed for noise reduction and spectral feature enhancement resulting in three datasets for each spectral region as follows: filtered only, filtered followed by extraction of the first derivative, and continuous wavelet transformation (CWT). Data reduction was then applied to these data sets using principal components analysis (PCA). The outputs obtained from the PCA were used to conduct the supervised classification of liana and tree leaves. In total, 21 classifiers were applied to datasets of training and testing to extract the classification accuracy and agreement for liana and tree leaves. The results suggest that the classification of leaves based on LWIR data can reach accuracy values between 66 and 96% and agreement values between 32 and 92%, regardless of the type of classifier. In contrast, the classification based on VIS-NIR data shows accuracy values between 50 and 70% and agreement values between 0.01 and 40%. The highest classification rates of liana and tree leaves were obtained from datasets pre-processed using the CWT or from the extraction of the first derivative and classified using either random forest, k-nearest neighbor, or support vector machine with radial kernel. The results using the LWIR reflectance highlight the potential of this spectral region for the accurate detection of liana extent in tropical ecosystems. Future studies should consider this potential and test the regional monitoring of lianas.

Reflectance spectroscopy and geochemical analysis of rare earth element-bearing tailings: A case study of two abandoned tin mine sites in Bangka Island, Indonesia

Rare Earth Elements (REEs) are indispensable in the manufacturing of renewable energy and clean technologies. Due to the high demand for REEs, mine waste, called “tailings”, are sought because they could be a possible resource for REEs. In this study, tailing samples were collected from two tin mine tailings in Bangka Island, Indonesia, and analyzed using inductively coupled plasma optical emission spectrometry, x-ray powder diffraction, and Fourier transform infrared - attenuated total reflectance. Results showed that the tailing samples were identified as quartz and contained a high amount of erbium between 111.6 and 3768.4 μg/g. Absorption features in infrared reflectance spectra were related to REE concentrations. We found a positive correlation between erbium and two absorption features that have not been reported before: One feature is centered at 500 nm with a correlation of 0.685, and one is centered at 674 nm with a correlation of 0.829.

INFLUENCE OF FORMATION OF THE COMPLEXES WITH DIFFERENT KIND OF LIGANDS ON KINETICS OF OXIDATIVE DISSOLUTION OF METALS

Rotating disk method has been used to study the dissolution of gold in the presence of an oxidizer and a mixture of dissimilar ligandforming reagents. Kinetic regularities of gold dissolution were investigated in aqueous systems thiourea-thiocyanate with Fe (III) and Cu (II) ions as the oxidizer; thiosulfate-thiocyanatewithFe(III)EDTA oxidizing complex and thiosulfate-thiocyanate with ammonia complex [Cu(NH3)4]2+ asoxidizing agent. Peculiarities of these mixed systems is a possibility to form the monoligandas as well as geteroligand complexes of gold. The influence of gold complexes formation with different sorts of ligands on the metal dissolution rate have been considered. The dependence of the dissolution rate on the ratio of ligands concentrations and on the oxidizing agent nature was investigated. Interrelation was established: the use of dissimilar ligandforming reagents - the higher thermodynamic stability of the geteroligand complexes of gold (relative to the homoligand ones) - synergistic increase of the gold dissolution rate. It was found that the heterophase reaction makromechanism for the thiourea-thiocyanate-Fe(III) system is determined by the proximity of the rates of chemical and diffusion stages (experimental activation energy - 21.6 kJ/mol; the reaction order in respect to the disk rotation frequency – 0.23). Diffusive limitation is due to the slow withdrawal of the reaction products -Au (I) compounds - from the solid phase surface. The formation of stronger heteroligand complexes and the corresponding increase in the reaction products concentration at the surface increases a rate of the metal diffusion into the solution. For the thiourea-thiosulfate-Fe(III)EDTA system a film formation of the reaction solid products on the gold surface was observed. To identify it the infrared reflection spectra of the polished gold surface after the etching were obtained. There is a strong absorption band on the spectra at 804 cm-1. Absorption in this area has been associated with the stretching vibrations of C=S bond of the thiourea molecules joined to the surface and the products of their oxidation.

Surface optical phonon – Plasmon interaction in nanodimensional CdTe thin films

Structural and optical properties of CdTe thin films were investigated applying atomic force microscopy (AFM), XRD powder technique, Raman spectroscopy and far–infrared spectroscopy. CdTe thin films were prepared by using thermal evaporation technique. In the analysis of the far – infrared reflection spectra, numerical model for calculating the reflectivity coefficient for system which includes films and substrate has been applied. Effective permittivity of film mixture (CdTe and air) was modeled by Maxwell – Garnet approximation. We reveal the existence of surface optical phonon (SOP) mode and coupled plasmon-SOP modes (CPSOPM).

Spectral reflectance indices sense desiccation induced changes in the thalli of Antarctic lichen Dermatocarpon polyphyllizum

Lichens, in polar and alpine regions, pass through repetitive dehydration and rehydration events over the years. The harsh environmental conditions affect the plasticity of lichen’s functional and structural features for their survival, in a species-specific way, and, thus, their optical and spectral characteristics. For an understanding on how dehydration affects lichens spectral reflectance, we measured visible (VIS) and near infrared (NIR) reflectance spectra of Dermatocarpon polyphyllizum, a foliose lichen species, from James Ross Island (Antarctica), during gradual dehydration from fully wet (relative water content (RWC) = 100%) to dry state (RWC = 0%), under laboratory conditions, and compared several derived reflectance indices (RIs) to RWC. We found a curvilinear relationship between RWC and range of RIs: water index (WI), photochemical reflectance index (PRI), normalized difference vegetation index (NDVI), modified chlorophyll absorption in reflectance indices (MCARI and MCARI1), simple ratio pigment index (SRPI), normalized pigment chlorophyll index (NPCI), and a new NIR shoulder region spectral ratio index (NSRI). The index NDVI was initially increased with maxima around 70% RWC and it steadily declined with further desiccation, whereas PRI in-creased with desiccation and steeply falls when RWC was below 10%. The curvilinear relationship, for RIs versus RWC, was best fitted by polynomial regressions of second or third degree, and it was found that RWC showed very high correlation with WI (R2 = 0.94) that is followed by MCARI (R2 = 0.87), NDVI (R2 = 0.83), and MCARI (R2 = 0.81). The index NSRI, proposed for accessing structural deterioration, was almost invariable during dehydration with the least value of the coefficient of determination (R2 = 0.28). This may mean that lichen, Dermatocarpon polyphyllizum, activates protection mechanisms initially in response to the progression of dehydration; however, severe dehydration causes deactivation of photosynthesis and associated pigments without much affecting its structure.

Microwave dielectric properties and infrared reflectivity spectra analysis of two novel low-firing AgCa2B2V3O12 (B = Mg, Zn) ceramics with garnet structure

Two Ag-containing microwave dielectric ceramics AgCa2B2V3O12 (B = Mg, Zn) with garnet structure were prepared through solid-state reaction method. Dense ceramics were obtained at low sintering temperatures, 665 °C for AgCa2Zn2V3O12 and 730 °C for AgCa2Mg2V3O12. Their microwave dielectric properties were characterized for the first time and analyzed by means of packing fraction, bond valence, octahedral distortion, Raman spectra and infrared reflectivity spectra. Both compounds displayed high chemical compatibility with Ag electrodes. Additionally, thermally stable ceramics with near-zero temperature coefficients of resonance frequency (τf) were achieved by forming ceramic composites with CaTiO3.

Comparative study on the physical properties of transition metal-doped (Co, Ni, Fe, and Mn) ZnO nanoparticles

Nano-crystalline of TM-doped ZnO with general formula Zn0.97TM0.03O (TM: Mn, Fe, Co, and Ni) was prepared using sol–gel method. The dependence of crystal structure, morphology, and optical and magnetic properties on the type of transition metals was investigated. The XRD investigation of pure and TM-doped ZnO nanoparticles samples confirms the formation of single-phase hexagonal wurtzite structure. The estimated crystallite sizes are found in the range of 17 and 38 nm for the doped and pure samples, respectively. The obtained data suggest that the dopant type plays a vital role in the physical properties of the investigated samples. The optical band-gap energy Eg has been calculated from near infrared (NIR) and visible (VIS) reflectance spectra using the Kubelka–Munk function. Minimum value of 2.398 eV and maximum one of 3.29 eV were obtained for Manganese-doped ZnO and pure ZnO, respectively. The analysis of XRD and VSM of the samples confirms that the observed room-temperature (RT) ferromagnetism can be attributed to an intrinsic property of doped material sample and not due to formation of any secondary phase. The magnetic results show that Mn is the most effective dopant for producing ferromagnetism in nanoparticles of ZnO.

Phonon modes, dielectric properties, infrared reflectivity, and Raman intensity spectra of semiconducting silicide BaSi2: First principles study

In this study, we investigated the phonon modes, dielectric properties, infrared (IR) reflectivity, and Raman intensity spectrum of semiconducting silicide BaSi2 within the framework of the first principles density functional theory. The zone-center phonon mode frequencies formed two major bands in the ranges of 50–150 cm−1 and 270–500 cm−1. The modes in the frequency band 100–150 cm−1 had high Born effective dynamical charges and oscillator strengths, and they contributed significantly to the mode effective charge, static dielectric permittivity, IR activities, and reflectivity spectrum. These modes were attributable to displacements of isolated Si clusters relative to one another without internal distortions. The computed Raman activities and intensities were significant for modes in the frequency band of 270–500 cm−1. These modes were primarily associated with silicon atom vibrations in the Si clusters in BaSi2 and the internal modes of the isolated Si clusters with Td symmetry. The band gap was also computed for BaSi2 using the modified Becke–Johnson exchange potential and it was in good agreement with the previously reported experimental values. The computed Raman intensity and IR reflectivity spectrum can be used as benchmark first principles theoretical results to compare with experimental results.