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In order to study the effect of MgO on the microstructure and macroscopic thermos-physical properties of calcium silicate melt, quantitative analysis of the various silicon-oxygen Qi species in magnesium-calcium silicate glasses and melts at a constant alkalinity has been performed by in-situ high temperature Raman spectroscopy, 29Si MAS NMR and DFT (Density Functional Theory) calculation. Several cluster models, probably existed in magnesium-calcium silicate glasses and melts, modified by Ca2+ or Mg2+ have been designed, their Raman vibrational modes and scattering activities were thus simulated and calculated. A function correlating the wavenumbers of Si-Onb (non-bridge oxygen) of various SiOTs (silicon-oxygen tetrahedrons) with their RSCS (Raman scattering cross sections) was constructed and used to calibrate the experimental Raman spectra. The abundance of each primary Qi species of various magnesium-calcium silicate glasses can be composed by all the deconvoluted hyperfine peaks within the same Qi species. The quantitative description for glasses was proven to be consistent with the result from 29Si MAS NMR. Thus, Qi species distributions for melts were also quantitatively derived. It demonstrated that the abundances of Q1 and Q3 species increased while Q2 species decreased with the increasing replacing amount of MgO. The relationship between the viscosity and Qi species distributions as well as different cations has been investigated and correlated. Q3 species was predominantly responsible for the contribution of viscosity of melt. more...

The 15 μm residual absorption of the BaGa4Se7 crystal is related to the OSe defect and originates from the deforming vibration of Ga–O–Ga bonds.

This work provides a promising theoretical methodology to solve the most fundamental problem in flux crystal growth.

Stimulated Raman scattering processes based on Raman crystals offer a simple and effective method to generate mid-IR lasers. However, currently available mid-IR Raman crystals are extremely scarce. Herein, a new type of mid-IR Raman crystal, BaGeO3, is reported. It crystallizes in the monoclinic space group C2/c with Ba2+ cations and [Ge3O9]6- rings as basic building units and features high transparency from 2.5 to 5.5 μm and a Raman response larger than that of diamond. The BaGeO3 crystal has 45 IR-active modes (22Au + 23Bu) and 42 Raman-active modes (20Ag + 22Bg). The wide mid-IR transparent window is attributed to the low phonon energy of the second-order IR-active Au ⊗ Bg mode. The strongest Raman band, located at 799 cm-1, arises from the symmetrically stretching vibration of the [Ge3O9]6- extra-ring Ge-O bonds. The findings provide new insights into the crystallographic and Raman spectroscopic characteristics of high-performance mid-IR Raman crystals. more...

Birefringent crystals are often applied to manipulate polarized states of light, yet the birefringent crystals used in the important mid-IR region are scarce. α-BaGeO3 is a potential mid-IR birefringent crystal due to its high mid-IR transmittance and strong structural anisotropy. Here, on the basis of density functional theory (DFT) calculations, we report the refractive characteristics of α-BaGeO3. The crystal is a positive biaxial crystal with the optical principal axes x, y and z parallel to the crystallographic b axis, 2.5° off the a axis, and 19.3° off the c axis, respectively. In the mid-IR region, the principle refractive indices nx, ny and nz are about 1.6297, 1.6308, and 1.6848, respectively. The maximum birefringence is about 0.055 which emerges when a light beam propagates along the x axis. These results indicate that the α-BaGeO3 crystal is a promising birefringent crystal used in the mid-IR region. Interestingly, α-BaGeO3 is quite similar to a uniaxial crystal in refractive characteristics, which is due to its unique layer structure. The refractive characteristics of α-BaGeO3 are associated with the Ba–O bonds; their spatial orientations determine the optical anisotropy of the crystal. more...

Knowledge of the molecular-level structure of the Li2GeO3 melt is essential to understand its basic physicochemical properties. In this work, in situ Raman spectroscopy, factor group analysis, and ... more...

In order to assist in predicting the properties of molten cryolite-alumina electrolytes widely used in the Hall–Heroult process, the micro-structure of the molten binary system was investigated by in situ high temperature Raman spectroscopy from room temperature to 1273 K under an argon atmosphere. The symmetric stretching vibrational wavenumbers of possible clusters in the molten system were further calculated through quantum chemistry ab initio simulations and compared with the experimental Raman spectra of the molten system. The molten K3AlF6–Al2O3 system was found to consist of [AlF5]2−, [AlF6]3−, [Al2OF6]2− and [Al2O2F4]2− clusters. With the increasing addition of Al2O3 to molten K3AlF6, the structure of six-coordinated Al atoms connected by terminal fluorine is partly believed to evolve into a structure of two four-coordinated Al atoms connected by single-bridging oxygen. The mole percentage of the species in the melt was also calculated from the experimental Raman spectra. As the Al2O3 content increased from 0 to 8.0 wt%, the content of [Al2OF6]2− in the melt was found to increase swiftly from 0 to 33.0 mol%, while the [Al2O2F4]2− content decreased after reaching a maximum of 1.5 mol%. more...

The Li2Mo4O13 melt structure and its Raman spectral characteristics are the key for establishing the composition–structure relationship of lithium molybdate melts. In this work, Raman spectroscopy, factor group analysis, and density functional theory (DFT) were applied to investigate the structural and spectral details of the H-Li2Mo4O13 crystal and a Li2Mo4O13 melt. Factor group analysis shows that the crystal has 171 vibrational modes (84Ag + 87Au), including three acoustic modes (3Au), six librational modes (2Ag + 4Au), 21 translational modes (7Ag + 14Au), and 141 internal modes (75Ag + 66Au). All of the Ag modes are Raman-active and were assigned by the DFT method. The Li2Mo4O13 melt structure was deduced from the H-Li2Mo4O13 crystal structure and demonstrated by the DFT method. The results show that the Li2Mo4O13 melt is made up of Li+ ions and Mo4O132– groups, each of which is formed by four corner-sharing MoO3O/MoO2O2 tetrahedra (O = bridging oxygen). The melt has three acoustic modes (3A) and 54 o... more...

In-situ high temperature Raman spectroscopic (HTRS) technique in combination with density functional theory (DFT) analysis has been adopted to investigate the micro-structure of solid and molten A2W2O7 (A = Li, Na, K). The [WO6] octahedra were found to be connected to each other by corner and edge sharing in the crystalline Li2W2O7 and K2W2O7 compounds. In the crystal lattice of Na2W2O7, on the other hand, the [WO4] tetrahedra and [WO6] octahedra were found to coexist and paired by corner sharing. Although the structural diversity has clearly led to distinct Raman spectra of the crystalline A2W2O7 compounds, the spectra of their melts tended to be analogous, showing the typical vibration modes of (W2O7)2 − dimer. A mechanism was then proposed to explain the structure evolution occurring during the melting process of A2W2O7. The effect of A+ cation on the Raman bands of (W2O7)2 − dimer in molten A2W2O7 has also been investigated. Both the wavenumber and full width at half-height (FWHH) of the characteristic band assigned to the symmetrical stretching vibration mode of W Onb (non-bridging oxygen) in (W2O7)2 − were found to decrease in the sequence of Li+, Na+ and K+, indicating the cation effect on the mean bond length and its distribution range of W Onb. In addition, the relative intensity of this band was also influenced by the cation and it was increased in the order of Li2W2O7, Na2W2O7 and K2W2O7, which has been explained by the charge transfer process and confirmed by Mulliken overlap population analysis. more...

Stimulated Raman scattering processes based on Raman crystals offer a simple and effective method to generate mid-IR lasers. However, currently available mid-IR Raman crystals are extremely scarce. Herein, a new type of mid-IR Raman crystal, BaGeO more...

LiB3O5 is the most widely used nonlinear optical crystal. Li2Mo3O10 (a nominal composition) is a typical flux used to produce large-sized and high-quality LiB3O5 crystals. The structure of the LiB3O5–Li2Mo3O10 high-temperature solution is essential to understanding the flux behavior of Li2Mo3O10 but still remains unclear. In this work, high-temperature Raman spectroscopy combined with density functional theory (DFT) was applied to study the LiB3O5–Li2Mo3O10 solution structure. Raman spectra of a LiB3O5–Li4Mo5O17–Li2Mo4O13 polycrystalline mixture were recorded at different temperatures until the mixture melted completely. The solution structure was deduced from the spectral changes and verified by DFT calculations. When the mixture began to melt, its molybdate component first changed into the Li2Mo3O10 melt; meanwhile, the complicated molybdate groups existing in the crystalline state transformed into Mo3O102– groups, which are formed by three corner-sharing MoO3O–/MoO2O2 (O = bridging oxygen atom) tetrahe... more...

LiB3O5 crystals are often grown from the Li2O·4B2O3 high-temperature melt. Information about the melt structure is essential for interpreting the macro-properties of the melt and investigating the micro-process of LiB3O5 crystal growth, but it still remains unknown. In this work, a method combining Raman spectroscopy and density functional theory (DFT) was employed to determine the Li2O·4B2O3 melt structure. The results show that B3O4O2 (O = bridging oxygen) and B3O3O3 rings are the main species present in this melt. A small number of BO4 units and BO double bonds were also found in the Li2O·4B2O3 melt. The BO4 units are formed via the connection of the non-bridging oxygen atoms in the B3O4O2 rings to the boron atoms in the neighbouring B3O3O3 rings; the BO bonds are formed by the breakage of the B3O3O3 rings. The structure has been used to interpret the high viscosity and the viscosity anomaly phenomenon of the Li2O·4B2O3 melt and to understand the micro-process of LiB3O5 crystal growth. more...

The quantitative distribution of different Qi species in binary calcium silicate glasses and their melts has been investigated by in-situ high temperature Raman spectroscopy, 29Si MAS NMR and quantum chemistry (QC) ab initio calculations. The structural units and several cluster structure models have been designed, optimized and calculated by ab initio calculations. The attribution of their vibrational modes, vibrational wavenumbers of non-bridging silicon-oxygen (Si-Onb) and Raman scattering cross sections (SCS) have then been worked out and analyzed. The functional relationship between the SCS and stress index of silicon-oxygen tetrahedron (SIT) was established for the model clusters of delicate Qi. Quantitative distributions of Qi in calcium silicate glasses and melts are finally obtained which are in good agreement with the experimental results of 29Si MAS NMR. Although the primary structure present in calcium silicate glasses and melts is the same, the relative distribution of Qi is different. On the basis of the present work, it will be helpful to predict the physicochemical properties of silicate slag. more...

Knowledge of the molecular-level structure of the Li

In situ high temperature X-ray diffraction and Raman spectroscopy were used to investigate the temperature dependent micro-structure of KAlF4. Density functional theory was applied to simulate the structure of crystalline KAlF4 while a quantum chemistry ab initio simulation was performed to explore the structure of molten KAlF4. Two crystal polymorphs demonstrated to be present in solid KAlF4. At the temperature below 673 K, it belongs to the tetragonal crystal system within the P4/mbm space group, while the high temperature phase is attributed to the monoclinic crystal system within the P21/m space group. Both polymorph KAlF4 phases are characterized by a layered structure consisting of K+ and [AlF6]3− octahedra, each of the [AlF6]3− octahedra equivalently shares four corners with other four [AlF6]3− octahedra along the layer. The layered structure became unstable at higher temperatures and crashed when the temperature exceeded the melting point. It demonstrated that the molten KAlF4 consisted of predominant [AlF4]− and a small amount of [AlF6]3−. The Raman spectrum of molten KAlF4 simulated by using a quantum chemistry ab initio method agreed well with the experimental Raman spectrum. more...

The quantitative distribution of different species ( Q ijklm and H ijklmno) in binary potassium molybdate melts has been investigated by in situ high temperature Raman spectroscopy in conjunction with quantum chemistry (QC) ab initio calculations. The symmetric stretching vibrational wavenumbers of molybdenum nonbridging oxygen bonds in high wavenumber range and their respectively corresponding Raman scattering cross sections were determined and analyzed. Deconvolution of the stretching bands of molybdenum nonbridging oxygen bonds of molten Raman spectra by using the Voigt function was carried out. The six-coordinated molybdenum oxygen octahedra [MoO6]6- have been proposed to be present in molten molybdates, apart from the well-known existence of the four-coordinated [MoO4]2- tetrahedra. The quantitative analysis of different species in the molten K2MoO4-MoO3 system and their dependence on the content of MoO3, as well as the relationship with the viscosities of the melts, were also discussed. The quantitative results have been integrated with published data on physical and chemical properties of the melts. more...

Raman spectroscopy at high temperature has been applied to study in situ the microstructure of the solution in a Cs2O–B2O3–MoO3 growth system. A crystal–solution interface was observed. The BO groups consist of spiral chains based on B3O4Ø2 rings in the solution (Ø is a bridging O atom). The Raman spectrum of the solution indicates that MoO4 tetrahedra existed in the growth system. The nonbridging O atoms of the chains combined with the MoO4 groups, which decreased the viscosity. The Raman spectra near the interface show that at the boundary an isomerization reaction from three- to four-coordinated boron occurred. The formation of B3Ø7 triborate groups occurred. The morphology of the CsB3O5 crystal resulting from spontaneous crystallization was observed to correspond to our expectations. more...

Raman spectroscopy has been applied to investigate in-situ the phase transition of a LBO (LiB 3 O 5 ) crystal near its melting point in order to explain the discrepancies between the experimental results observed in the LBO crystal growth process and the predicted results obtained from the Li 2 O–B 2 O 3 phase diagram. When the LBO crystal begins to melt, it first decomposes to the kinetic products Li 2 B 4 O 7 and B 2 O 3 ; then the Li 2 B 4 O 7 reacts with the undecomposed LBO to form the thermodynamic product Li 3 B 7 O 12 . On the basis of these results, a set of models have been proposed to describe the structural transformations present in the phase transition. Additionally, our experimental result indicates that Li 3 B 7 O 12 is stable/metastable at room temperature. Its Raman spectrum has been calculated by the density functional theory method for identification of the Li 3 B 7 O 12 crystalline phase in a mixture. The result shows that Li 3 B 7 O 12 has three strong characteristic Raman peaks located around 595, 775 and 1040 cm −1 . more...

Ba 2 Pb(B 3 O 6 ) 2 polycrystalline powder was synthesized by a solid state reaction using BaCO 3 , Pb 3 O 4 and H 3 BO 3 as initial reactants. The crystal structure was solved from the powder X-ray diffraction data by the Rietveld refinement method and the DFT (density functional theory) calculation. The results show that Ba 2 Pb(B 3 O 6 ) 2 is isostructural with the high-temperature phase BaB 2 O 4 (Ba 2 Ba(B 3 O 6 ) 2 ). It crystallizes in the trigonal space group R 3 ¯ c with a = b = 7.20295(3) A, c = 37.594(1) A, and Z = 6. The structure is built up of the layers of B 3 O 6 rings that are separated by Ba 2+ or Pb 2+ cations. The Raman spectrum of Ba 2 Pb(B 3 O 6 ) 2 was interpreted on the basis of the analysis through site group method. Its irreducible representation of the normal modes is 10 A 1g + 11 A 2g + 10 A 1u + 11 A 2u + 21 E g + 21 E u among which 10 A 1g + 11 A 2g + 10 A 1u + 10 A 2u + 21 E g + 20 E u are optical modes, where the A 1g and E g are Raman active. The DFT calculated results confirmed the results of the site group analysis and assigned all peaks in the experimental Raman spectrum. The α-BaB 2 O 4 Raman spectrum was recorded and compared with the Ba 2 Pb(B 3 O 6 ) 2 Raman spectrum. The effect of the Pb 2+ cations on the Raman intensity was discussed. more...

Lithium triborate (LiB3O5, LBO) is the most widely used nonlinear optical crystal. During the LBO crystal melting process, several interesting and important phenomena, called as structural memory, have been found. However, the essence of these phenomena remains unclear. In order to explain these phenomena, high-temperature Raman spectroscopy was used to investigate in situ the structures of a LiB3O5 melt at different temperatures. Two important structural transformations were found during the LBO crystal melting process: (1) when the crystal begins to melt, every two adjacent basic building units (B3O4O2) in the crystal structure transforms to a B4O5O4 group and a B2O3 molecule. (2) Above 860 °C, the B4O5O4 units react with the B2O3 molecules to form boron–oxygen chains whose minimal repeated unit is the B3O4O2 six-membered ring. These results prove that LBO is an incongruently melting compound and provide a rationale for understanding the special structural memory phenomena. more...

A melt structure is an intrinsic factor used to govern a variety of melt macro-properties and plays a fundamental role in understanding crystal growth mechanisms. In this paper, high-temperature Raman spectroscopy and a density functional theory (DFT) method were used to investigate the structure of a K2O-rich KNbO3 (KN) melt which was in equilibrium with a KN crystal. K+ ions and isolated NbO3− groups have been found to be the main structural units in the bulk melt. The NbO3− units connect with each other near the crystal–melt interface to form NbO2O2− (O = bridging oxygen) chains that further form NbO6− octahedra (the basic units in the KN crystal structure) on the crystal–melt interface. A boundary layer with the thickness of about 5 μm was observed around the interface. The DFT calculations verified the melt structures and provided accurate assignments for the vibrational bands present in the melt Raman spectra. more...

Ba 2 M(B 3 O 6 ) 2 (M = Mg, Ca and Ba) are potential stimulated Raman scattering (SRS) crystals. Their Raman spectral peak positions that determine the SRS laser wavelengths are influenced by the M cations. When M is replaced in the order of Mg, Ca and Ba, all internally vibrational peaks red-shift except the peak below 600 cm −1 . First-principles method was used to interpret the M cation effect. The calculated results show that the B–O bond populations decrease with the increase of the alkali-earth cation (Ba and M) populations in the order of Ba 2 Mg(B 3 O 6 ) 2 , Ba 2 Ca(B 3 O 6 ) 2 and Ba 2 Ba(B 3 O 6 ) 2 (α-BBO, high-temperature phase BaB 2 O 4 crystal), which weakens the B–O bonds and red-shifts the peaks arising from the internal modes. On the basis of the results, four important Raman vibrational peaks were discussed. The abnormal blue-shift of the peak located below 600 cm −1 is attributed to the Davydov splitting that originates from the interaction between two adjacent B 3 O 6 rings. The splitting energies ( Δ ) of the Ba 2 Mg(B 3 O 6 ) 2 , Ba 2 Ca(B 3 O 6 ) 2 and α-BBO crystals are 50 cm −1 , 38 cm −1 and 25 cm −1 , respectively. more...

The Li

High-temperature Raman spectroscopy has been applied to studyin situthe microstructure of the solution near the β-BaB2O4crystal–solution interface in the BaO–B2O3–Na2O growth system. A boundary layer near the crystal–solution interface was observed. In accordance with the high-temperature Raman spectroscopy and first principles calculations, a boron–oxygen structural model is proposed to explain the microstructure of the solution and growth habit. The results show that the growth solution contains a special group, [BO2ØBOØB=O]3−(Ø = bridging oxygen), which transformed to the growth unit [B3O6]3−near the interface. more...

Melt structure, a fundamental and challenging subject for borate crystal growth, has not been solved for many years. In this paper, a new method has been employed to study the Li2B4O7 melt structure. High-temperature Raman spectroscopy has been used to investigate the structural evolvement from a Li2B4O7 crystal to a Li2B4O7 melt. Based on the investigation, a model was proposed to describe the Li2B4O7 melt. The melt is made up of polymer-like boron–oxygen chains; the minimal repeated unit is the B4O6O22− (O = bridging oxygen) group which is formed by a B3O4O2− six-membered ring and a BOO2− triangle linked by a bridging oxygen atom. DFT calculations have verified the melt structure and provided accurate assignments for the vibrational bands present in the Li2B4O7 melt Raman spectrum. more...

In-situ high temperature Raman spectroscopic (HTRS) technique in combination with density functional theory (DFT) analysis has been adopted to investigate the micro-structure of solid and molten A

LiB

The structure of borate melt has long been a fundamental unsolved problem in condensed matter physics, materials chemistry. Here, we use high temperature Raman spectroscopy and first principles calculations to study the structural change before and after the melting of a BiB3O6 crystal to obtain the BiB3O6 melt structure. A transformation of the 4-fold coordinated boron atoms to 3-fold coordinated boron atoms and a destruction of the atomic configuration around the Bi3+ ions were found when the crystal melted. Considering the growth habit of the BIBO crystal, we proposed a polymer model for the first time to describe the melt structure. The BiB3O6 melt is made up of special [B3O3O3] (O = bridging oxygen) structural units, which further polymerize into [B3O3O3]n chains by sharing oxygen atoms; the boron–oxygen chains are surrounded by the Bi3+ ions. Density functional theory (DFT) calculations were carried out to simulate the melt Raman spectrum based on the structural unit. The calculated BiB3O6 melt Raman spectrum shows good agreement with the experimental spectrum. The main vibrational bands were assigned. The strongest band below 400 cm−1 is mainly attributed to the wagging vibration of the side BOO2 triangle as a whole; the band located around 630 cm−1 is assigned to the bending vibrations of the [B3O3O3]n chain; the bands in the range of 1200–1500 cm−1 arise from the stretching vibrations of B–O (or B–O) bonds in the boron–oxygen triangles. more...

MoO3 is an important flux for lithium triborate (LiB3O5) crystal growth from high-temperature solutions. Although it has been widely used, the mechanism of the MoO3 flux-induced growth of LiB3O5 crystals is still not very clear. In this paper, we present a spectroscopic investigation of the Li2O–B2O3–MoO3 ternary glasses/solutions, which were prepared from high-temperature MoO3-based solutions for LiB3O5 crystal growth. By combining all the experimental data of Raman and MAS NMR, the types of structural species and the interactions between flux and solute are discussed to understand the MoO3 flux-reduced mechanism of LiB3O5 crystallization from the high-temperature solution. Considering the activities of lithium cations, an isomerization reaction is proposed to describe the structural evolution of the BO4 tetrahedron into the BO3 triangle in boroxol due to the MoO3 flux. The transition between the boron oxide species is essential for the LiB3O5 crystal growth. On cooling, the formed boroxol rings are polymerized by the re-formation of BO4 tetrahedrons again, and gather together to form the LiB3O5 crystal phase. Finally, the MoO3 flux-induced LiB3O5 crystallization may be elucidated with the decrease of the concentration of the BO4 tetrahedron in high-temperature solutions. more...

Melt structures are essential to understand a variety of crystal growth phenomena of alkali-metal triborates, but have not been fully explored. In this work, Raman spectroscopy, coupled with the density functional theory (DFT) method, has been used to solve the CsB3O5 (CBO) melt structure. When the CBO crystal melts, the extra-ring B4–O bonds (the B–O bonds of BO4 groups, O = bridging oxygen atom) that connect two B3O3O4 rings (the basic boron–oxygen unit in the CBO crystal structure) break. As a result, the three-dimensional boron–oxygen network collapses to unique polymer-like [B3O4O2]n chains. On the basis of the optimized [B3O4O2]n chain model, the CBO melt Raman spectrum was calculated by the DFT method for the first time and the calculated results confirm that the [B3O4O2]n chain is the primary species in the CBO melt. These results also demonstrate the capability of the combined Raman spectral and DFT method for analyzing borate melt structures. more...

Nano-Cu 3 VS 4 thin films were prepared by pulsed laser deposition (PLD) method; the fundamental optical and electrical properties were studied in order to evaluate its application prospect as an absorbing layer material for use in thin film solar cells. The optimal nano-Cu 3 VS 4 thin film was deposited at 500 °C (the substrate temperature) for 40 min with a pulsed KrF laser (5 Hz, 120 mJ/pulse). The obtained thin film is black, homogeneous with good adherence to the substrate; the average crystallite size is about 23 nm. The bandgap of the nano-Cu 3 VS 4 thin film, determined from the spectroscopic ellipsometry data, was found to be 1.35 eV. Its absorption coefficients are larger than 10 5 cm −1 when the wavelength is shorter than 720 nm. The nano-Cu 3 VS 4 has a near direct bandgap structure which is different from the bulk Cu 3 VS 4 . Its dark conductivity is about 1.88 Ω −1 cm −1 at room temperature and the calculated conductivity activation energy is around 24 meV. All of the optical and electrical behaviors show that the nano-Cu 3 VS 4 is a potential absorbing layer material for use in the thin film solar cells. more...

Raman spectroscopy is a powerful tool to judge the fundamental building units contained in crystal structure. In this work, it was used to investigate the basic structural groups involved in the low temperature (LT) and high temperature (HT) phase YBO 3 . The characteristic Raman vibrational bands of the LT and HT phases YBO 3 were identified respectively. The characteristic vibrational peaks of the LT phase YBO 3 locate around 410 cm −1 and 500 cm −1 , both of them are attributed to the ring bending modes of B 3 O 9 group. The strong characteristic vibrational band of the HT phase YBO 3 , arising from the symmetric stretching mode of BO 3 group, locates around 940 cm −1 . A structural phase transition with a large thermal hysteresis was found. During the phase transition process, the B–O bonds of the BO 4 groups break and the B 3 O 9 rings cleave into the BO 3 plane conjugated groups. more...

The fundamental properties of CdFe2O4 semiconductor thin film have been investigated. CdFe2O4 polycrystalline powder was synthesized by a co-precipitation–calcination process, and its thin film was prepared on a glass substrate by the pulsed laser deposition (PLD) method. The transmittance and reflectance spectra of the thin film indicate that the compound is an indirect bandgap material with E g = 1.97 eV. Its absorption coefficients are larger than 104 cm−1 when the wavelength is shorter than 700 nm. The electrical conductivity of the CdFe2O4 thin film was measured at different temperatures, its conductivity activation energy is about 71.9 meV. The relationship between CdFe2O4 semiconductor properties and its microstructure was discussed. more...

High-temperature Raman spectroscopy has been applied to investigate the melt structure near the BiB3O6 (BIBO) crystal–melt interface. Based on the experimental results, the crystal growth mechanism was proposed. (BOO)n (O = bridging oxygen atom) chains and free Bi3+ cations present in the BIBO bulk melt act as the crystal growth units. Bi-O bonds and [BO4]-tetrahedra were found near the BIBO crystal–melt interface. Two neighboring oxygen atoms in a (BOO)n chain or in two different (BOO)n chains are connected by the Bi3+ cations to form the structural prototype of BIBO crystal. Two adjacent (BOO)n chains are further connected to each other through the [BO4] tetrahedra to form the BIBO crystal structure. The predicted growth habit of the BIBO crystal is consistent with the observed one based on the mechanism. more...

The methods to synthesize Eu:YAG phosphor by co-precipitation method and solid-state synthesis were compared. The dynamic aspects of the phase transition of Eu:YAG precursor synthesized by co-precipitation method were studied by using X-ray diffraction, infrared and Raman spectroscopy. The results showed that the precursor transformed to pure-YAG phase at the sintering temperature of 900 °C without intermediate phases present. Transmission electron microscope for the precursor powders sintered at 900–1200 °C showed that the powders were well-dispersed and had average size about 50–100 nm.The fluorescence spectra showed that the Eu:YAG phosphors had strong photoluminescence. The luminescence properties of the sintered powders depend on the sintering temperature were also analyzed. more...

Segregation during crystal growth from melt under two conditions is studied by using crystal mass, which can be measured easily, as an independent variable, and a method to determine the effective segregation coefficient and absorption cross section of optical dopant is given. When the segregated solute disperses into the whole or just a part of melt homogenously, the concentration Cs in solid interface will change by different formulas. If the crystal growth interface is conical and segregated solute disperses into melt in total or part, the solute concentration at r = 2/3R, where r is the distance from the growth cross section center and R the crystal radius, is independent on the shape of the crystal growth interface, and its variation at r = 2/3R can be regarded as the result from crystal growth in flat interface. With Cs variation formula in solid and absorption cross section σ for optical dopant, the absorption coefficients along the crystal growth direction can be calculated, and the corresponding experimental value can be obtained through the crystal optical absorption spectra. By minimizing the half sum, whose independent variables are k, ΔW or σ, of the difference square between the calculated and experimental absorption coefficients from one or more absorption peaks along the crystal growth direction, k and σ, or k and ΔW, can be determined at the same time through the Levenberg-Marquardt iteration method. Finally, the effective segregation coefficient k, ΔW and absorption cross sections of Nd:GGG were determined, the results fitted by two formula gave more closed effective segregation coefficient, and the value ΔW also indicates that the segregated dopant had nearly dispersed into the whole melt. Experimental results show that the method to determine effective segregation coefficient k, ΔW and absorption cross sections σ is convenient and reliable, and the two segregation formulas can describe the segregation during the crystal growth from melt relatively commendably. more...

The structure of the melt near a crystal–melt interface is a fundamental problem in the dynamics of crystal growth. In this work, high-temperature Raman spectroscopy was applied to investigatein situthe structure of the melt near the α-BaB2O4(α-BBO) crystal–melt interface. A structured melt was found in this region: (B3O6)3−groups form near the interface and vanish towards the bulk melt. The crystal growth habit was then explained by the periodic bond chain (PBC) theory. At the α-BBO crystal–melt interface, the growth units, namely the (B3O6)3−anion groups and Ba2+cations, stack mainly along four types of PBCs. These four PBCs constitute three potential F faces: {10\bar{1} 2}, {01\bar{1} 4} and {10\bar{1} 10}. The predicted results are in good agreement with the observed growth habit of α-BBO crystal. more...

CuBrSe3 has been synthesized by the reaction between CuBr2 and Se in ethylene glycol (EG) solvent at 100 °C. In the process, CuBr2 was reduced to brom-complexes of Cu(I), such as CuBr 2 - , the complexes participated in the reaction as intermediates. Based on experimental results and the structure characterization of CuBrSe3 crystal, a possible mechanism for CuBrSe3 formation was proposed. The mechanism suggests that Se chains assembly with the brom-complexes of Cu(I) to form CuBr helical chains, and then CuBrSe3 crystal. more...

Co9S8 hexagonal aggregations were synthesized in hydrazine hydrate (N2H4·H2O) solvent at 150 °C for 12 h using cobalt(II) sulfate hydrate (CoSO4·7H2O) and sodium sulfite (Na2SO3) as starting materi... more...

CuClSe2 was synthesized by solid-state reaction between copper chloride and selenium at 300 °C. CuClSe2 thin film was prepared on a glass substrate by pulsed laser deposition (PLD) method. XRD (X-ray diffraction) analysis revealed that the CuClSe2 thin film has a preferred surface orientation parallel to (006). The transmittance and reflectance spectra of the film indicated that the compound is an indirect band gap material; the energy band gap is about 1.45 eV; its absorption coefficients are in the range of 104–105 cm− 1 when the wavelength is shorter than 720 nm. The melting point of CuClSe2 is about 328 °C. These results show that CuClSe2 is a potential absorber layer material applied in solar cells. more...