首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 234 毫秒
1.
A series of (1 ? x)GeS2.5 – xSb chalcogenide glasses were prepared using the conventional melt‐quenching method. Their microstructure and thermal response were systematically studied. We observe a compositional threshold of x = 0.25 which corresponds to chemical stoichiometric composition in the calorimetric experiments. It is in good accordance with the Raman scattering results and laser‐induced phase transformation behavior. They also indicate that phase separation of Sb‐rich phase exists in the S‐poor samples. Moreover, we got a structural modeling of this phase separation: (1) at x = 0.25, which is chemical stoichiometric composition, the structural motifs are only SbS3 pyramid and GeS4 tetrahedra, and the three‐coordinated SbS3 pyramid is isolated by GeS4 tetrahedra; (2) at x < 0.25, the S–S bonds exist in the glass network due to the excess of S; and (3) at x > 0.25, the excess of Sb break the Ge–S and Sb–S bonds to form Sb(Ge)–Sb Bonds, and the Sb atoms segregate from the backbone to nucleate a separate Sb‐rich phase. This work provides a new way to investigate the phase separation of glass networks and helps us to better understand their related physical properties.  相似文献   

2.
The structure of Te‐rich (75–80 at.% Te) and Te‐poor (40 at.% Te) Ge–As–Te glasses has been investigated by diffraction and extended X‐ray absorption fine structure (EXAFS) measurements. Large‐scale structural models have been created by fitting simultaneously diffraction and EXAFS datasets by the reverse Monte Carlo simulation technique. It is found that As–As bonds improve the fit quality in the case of Te‐rich glasses while no Ge–Ge bonding is necessary in these compositions. In the Te‐poor glasses, Te–Te homopolar bonds are also observed while Ge binds preferentially to Te rather than to As. Ge–As and Ge–Te coordination numbers do not change significantly with increasing Ge content.  相似文献   

3.
Pulsed laser deposition was used to prepare amorphous thin films from (GeSe2)100?x(Sb2Se3)x system (x = 0, 5, 10, 20, 30, 40, 50, and 60). From a wide variety of chalcogenide glass‐forming systems, Ge–Sb–Se one, especially in thin films form, already proved to offer a great potential for photonic devices such as chemical sensors. This system has a large glass‐forming region which gives the possibility to adjust the chemical composition of the glasses according to required physical characteristics. The chemical composition of fabricated thin films was analyzed via X‐ray photoelectron spectroscopy (XPS) and compared to energy dispersive spectroscopy (EDS) data. The results of both techniques agree well: a small deficiency in chalcogen element and an excess of antimony was found. The structure of as‐deposited thin films has been investigated by XPS. The presence of the two main structural units, [GeSe4] and [SbSe3] proposed by Raman scattering spectroscopy data analysis, was confirmed by XPS. Moreover, XPS core level spectra analysis revealed the presence of M–M bonds (M = Ge, Sb) in (Ge,Sb)–Ge–(Se)3 and (Ge,Sb)–Sb–(Se)2 entities that could correspond to Ge‐based tetrahedra and Sb‐based pyramids where one of its Se atoms at corners is substituted by Ge or Sb ones. The content of depicted M–M bonds tends to increase with introduction of antimony in the amorphous network of as‐deposited thin films from x = 0 to x = 40 and then it decreases. XPS analysis of as‐deposited thin films shows also the presence of the (Ge,Sb)–Se–(Ge,Sb) and Se–Se–(Ge,Sb) entities.  相似文献   

4.
A series of (GeTe4.3)100?x(AgI)x (x = 5, 10, 15, 20, 25, 30 mol%) chalcohalide glasses was prepared to investigate their potential in acousto-optic (AO) materials. Detailed thermal and optical properties of these glasses have been analyzed by DSC, XRD and FTIR. Meanwhile, refractive index, density, elastic modulus, acoustic velocity and attenuation, and the AO figure of merit (M2) were also reported. The results indicated that all these glasses presented a single glass transition temperature (Tg) and a single crystallization peak (Tx), and Tg decreases while Tx increases with the addition of AgI. X-ray power diffraction investigation showed the amorphous state of these synthesized glasses. They all have a wide transparent window from 2 to 20 μm, and acoustic attenuation was observed almost linearly proportional to the frequency at room temperature. Furthermore, refractive index and density increase, while acoustic velocity and elastic modulus decreases monotonously upon introducing AgI to GeTe4.3. The maximum refractive index (n = 3.729) and minimum acoustic velocity (V = 2.037 × 103 m/s) appeared in 70GeTe4.3–30AgI glass, thereby resulting in a maximum M2 of 3671 × 10?15 s3/kg at 10.6 μm. The outstandingly high M2 of this vitreous material make it attractive for far-infrared (FIR) AO modulators that require greater diffraction efficiency.  相似文献   

5.
Na‐ion conducting Na1+x[SnxGe2?x(PO4)3] (x = 0, 0.25, 0.5, and 0.75 mol%) glass samples with NASICON‐type phase were synthesized by the melt quenching method and glass‐ceramics were formed by heat treating the precursor glasses at their crystallization temperatures. XRD traces exhibit formation of most stable crystalline phase NaGe2(PO4)3 (ICSD‐164019) with trigonal structure. Structural illustration of sodium germanium phosphate [NaGe2(PO4)3] displays that each germanium is surrounded by 6 oxygen atom showing octahedral symmetry (GeO6) and phosphorous with 4 oxygen atoms showing tetrahedral symmetry (PO4). The highest bulk Na+ ion conductivities and lowest activation energy for conduction were achieved to be 8.39 × 10?05 S/cm and 0.52 eV for the optimum substitution levels (x = 0.5 mol%, Na1.5[Sn0.5Ge1.5(PO4)3]) of tetrahedral Ge4+ ions by Sn4+ on Na–Ge–P network. CV studies of the best conducting Na1.5[Sn0.5Ge1.5(PO4)3] glass‐ceramic electrolyte possesses a wide electrochemical window of 6 V. The structural and EIS studies of these glass‐ceramic electrolyte samples were monitored in light of the substitution of Ge by its larger homologue Sn.  相似文献   

6.
A novel method is employed for the formation of rare earth phosphate solid solution compounds with unique mesoscopic structures. Europium‐ and lanthanum‐doped sodium borate glass microspheres and particles, ranging in sizes from 50 to 300 μm, were reacted in 0.25 M K2HPO4 solution to form hollow spheres of nanocrystalline rare earth phosphate compounds by dissolution–precipitation reactions. The initially X‐ray amorphous precipitated rare earth phosphate materials were heat‐treated at 700°C for 2 h to form nanocrystalline compounds. Differential thermal analysis (DTA) experiments yield an average activation energy for crystallization of 394 ± 26 kJ/mol. X‐ray diffraction (XRD) data indicate that samples crystallized to the monazite structure (monoclinic P21/n) with unit cell volumes ranging from 306.5 Å3 for LaPO4 to 282.5 Å3 for EuPO4 and with crystallite grain sizes of 56 ± 14 nm. Compositions containing both rare earth elements formed solid solutions with the composition La(1?x)EuxPO4. Raman spectroscopy indicates that the P–O symmetric stretching vibrations (ν1) change systematically from 963 cm?1 for LaPO4 to 986 cm?1 for EuPO4, consistent with a systematic decrease in average P–O bond length. Photoluminescence measurements show maximum emission intensity for the La0.65Eu0.35PO4 composition.  相似文献   

7.
For the first time, the Raman spectra of bulk SexTe1‐x glasses, 0.5 ≤  1.0, have been measured over the entire glass‐forming range. The spectra exhibit three broad spectral features between 150 and 300 cm?1, attributed to Te–Te, Se–Te, and Se–Se stretching modes according to DFT simulations. The observed weak chemical ordering in the glasses is discussed on the basis of heteropolar and homopolar bond fractions derived from integrated intensity of the Raman modes and DFT cross‐sections. The underlying structural model of the glasses suggests a random distribution of the Se–Se, Se–Te, and Te–Te chemical bonds with some preference for heteropolar bonding within Se–Te–Se structural units.  相似文献   

8.
Two intermediate compounds of the system Ca2SiO4Ca3(PO4)2CaNaPO4 were synthesized by reaction sintering at 1600°C and analyzed structurally, chemically, and optically. The structure of Ca7(PO4)2(SiO4)2 nagelschmidtite (space group P61, a = 10.7754(1) Å, c = 21.4166(3) Å) was determined by single crystal X‐ray analysis. Its unit cell can be interpreted as a supercell (≈ × a, 3 × c) of the high‐temperature polymorph α‐Ca2SiO4. Evidence for pseudo‐hexagonal symmetry is shown. Using electron microprobe, the solid solution Ca7?xNax(PO4)2+x(SiO4)2?x, (x ≤ 2), of nagelschmidtite was confirmed. Volume thermal expansion coefficients of Ca6.8Na0.2(PO4)2.2(SiO4)1.8 and Ca5.4Na1.5(PO4)3.7(SiO4)0.3 were determined using high‐temperature X‐ray powder diffraction, yielding mean αV = 3.95 and 5.21 [×10?5/°C], respectively. Ca15(PO4)2(SiO4)6 is a distinct phase in the binary section Ca2SiO4Ca3(PO4)2 and was found to extend into the ternary space according to Ca15?xNax(PO4)2+x(SiO4)6?x, (x ≤ 0.1). Quenching experiments of the latter allowed for structural analysis of a strongly disordered, defective high‐temperature polymorph of the α‐Ca2SiO4α‐Ca3(PO4)2 solid solution. Structural relations between nagelschmidtite, Ca15(PO4)2(SiO4)6 and the end‐member compounds of the system are discussed.  相似文献   

9.
Electrical measurements, dc and ac, show that (AgI)x(HgS)0.5‐x/2(As2S3)0.5‐x/2 glasses, 0.0 ≤   0.6, exhibit drastic changes in ionic conductivity σi with silver iodide additions. The ionic transport increases by 13 orders of magnitude with increasing silver content from ~0.002 to ~23 at.%, and the activation energy decreases from 1.05 to 0.35 eV. Two distinctly different ion transport regimes above the percolation threshold concentration, xc ≈ 30 ppm, were distinguished. The critical percolation regime at low silver content (≤ 2‐5 at.% Ag) is characterized by a random distribution of silver‐related entities and obeys a power‐law composition dependence of σi. The ion transport parameters depend on the host network connectivity, represented by the average coordination number <n0>, via the critical fictive temperature T0; the calculated T0 value is comparable to the glass transition temperature for the glassy (HgS)0.5(As2S3)0.5 host matrix. In contrast, in the modifier‐controlled domain, the silver‐related entities are nonrandomly distributed. The high Ag+ ionic mobility results from interconnected tetrahedral (AgI2/2S2/2)n chains in the silver iodide content range 0.2 <  0.5, and from 2D layers (Ag3/3I3/3)n or 3D mixed tetrahedral subnetwork (AgI3/3S1/2) in the range > 0.5.  相似文献   

10.
Highly c‐axis‐oriented Ca3Co4?xCuxO9+δ (= 0, 0.1, 0.2, and 0.3) thin films were prepared by chemical solution deposition on LaAlO3 (001) single‐crystal substrates. X‐ray diffraction, field‐emission scanning electronic microscopy, X‐ray photoelectron spectroscopy, and ultraviolet‐visible absorption spectrums were used to characterize the derived thin films. The solubility limit of Cu was found to be less than 0.2, above which [Ca2(Co0.65Cu0.35)2O4]0.624CoO2 with quadruplicated rock‐salt layers was observed. The electrical resistivity decreased monotonously with increasing Cu‐doping content when x ≤ 0.2, and then slightly increased with further Cu doping. The Seebeck coefficient was enhanced from ~100 μV/K for the undoped thin film to ~120 μV/K for the Cu‐doped thin films. The power factor was enhanced for about two times at room temperature by Cu doping, suggesting that Cu‐doped Ca3Co4O9+δ thin films could be a promising candidate for thermoelectric applications.  相似文献   

11.
Gallium (Ga) helps solubilize rare‐earth ions in chalcogenide glasses, but has been found to form the dominant crystallizing selenide phase in bulk glass in our previous work. Here, the crystallization behavior is compared of as‐annealed 0–3000 ppmw Dy3+‐doped Ge–As–Ga–Se glasses with different Ga levels: Ge16.5As(19?x)GaxSe64.5 (at.%), for x = 3 and 10, named Ga3 and Ga10 glass series, respectively. X‐ray diffraction and high‐resolution transmission electron microscopy are employed to examine crystals in the bulk of the as‐prepared glasses, and the crystalline phase is proved to be the same: Ge‐modified, face centered cubic α‐Ga2Se3. Light scattering of polished glass samples is monitored using Fourier transform spectroscopy. When Ga is decreased from 10 to 3 at.%, the bulk crystallization is dramatically reduced and the optical scattering loss decreases. Surface defects, with a rough topology observed for both series of as‐prepared chalcogenide glasses, are demonstrated to comprise Dy, Si, and [O]. For the first time, evidence for the proposed nucleation agent Dy2O3 is found inside the bulk of as‐prepared glass. This is an important result because rare‐earth ions bound in a high phonon–energy oxide local environment are, as a consequence, inactive mid‐infrared fluorophores because they undergo preferential nonradiative decay of excited states.  相似文献   

12.
We explored the structure and physical properties of Ge15Sb20Se65‐xSx (with x = 0, 16.25, 32.5, 48.75, and 65) glasses in order to screen the best compositions for the applications in photonics, since the laser damage thresholds in Se‐based glasses are too low although their optical nonlinearities are high. We found that, linear and nonlinear refractive index of the glasses decreased, but glass transition temperature Tg, optical bandgap Eg and the laser damage threshold increased with increasing S content. We further employed Raman scattering and high‐resolution X‐ray photoelectron spectra to probe the structure of the glasses. Through the analysis of the evolution of the different structural units in the glasses, it was concluded that, the heteropolar bonds (Ge–Se/S, Sb–Se/S) were dominated in these glasses. With the increase in chalcogen Se/S ratio, the number of the Se‐related chemical bonds (Ge–Se, Sb–Se and Se–Se) increased and that of S‐related chemical bond (Ge–S, Sb–S and S–S) decreased gradually, and Ge was prior to bond with S rather than Se. The elemental substitution thus had negligible effect on the glass structure. The change of the physical properties was mainly due to the difference of the strength of the chemical bonds between S–Ge(Sb) and Se–Ge(Sb).  相似文献   

13.
Using synchrotron X‐ray diffraction and diamond anvil cells we performed in situ high‐pressure studies of mullite‐type phases of general formula Al4+2xSi2?2xO10?x and differing in the amount of oxygen vacancies: 2:1‐mullite (= 0.4), 3:2‐mullite (= 0.25), and sillimanite (= 0). The structural stability of 2:1‐mullite, 3:2‐mullite, and sillimanite was investigated up to 40.8, 27.3, and 44.6 GPa, respectively, in quasi‐hydrostatic conditions, at ambient temperature. This is the first report of a static high‐pressure investigation of Al2O3–SiO2 mullites. It was found that oxygen vacancies play a significant role in the compression mechanisms of the mullites by decreasing the mechanical stability of the phases with the number of vacancies. Elevated pressure leads to an irreversible amorphization above ~20 GPa for 2:1‐mullite and above 22 GPa for 3:2‐mullite. In sillimanite, only a partial amorphization is observed above 30 GPa. Based on Rietveld structural refinements of high‐pressure X‐ray diffraction patterns, the pressure‐driven evolution of unit cell parameters is presented. The experimental bulk moduli obtained are as follows: K0 = 162(7) GPa with K0′ = 2.2(6) for 2:1‐mullite, K0 = 173(7) GPa with K0′ = 2.3(2) for 3:2‐mullite, K0 = 167(7) GPa with K0′ = 2.1(4) for sillimanite.  相似文献   

14.
This study investigates the enhanced structural, and optoelectronic properties of transparent conductive Ga‐doped MgxZn1 ? xO (GMZO) thin films with a varied magnesium (Mg) composition of 2% and 8%, respectively. The X‐ray diffraction (XRD) measurements revealed that GMZO with an 8% Mg composition shows a stronger (002) diffraction intensity and narrower linewidth than that with a 2% Mg composition. Improved crystallinity and enlarged grain size in the postgrowth thermal annealed GMZO thin films were also observed in XRD and morphological measurements by atomic force microscopy. Photoluminescence measurements were conducted to investigate the improved GMZO thin‐film quality, and the oxygen vacancy signal was found to decrease with increased Mg content, consistent with X‐ray photoelectron spectroscopy measurements. This study also shows high optical transmittance over 98%, and a low resistivity of 5.7 × 10?4 Ω·cm in Ga‐doped MgxZn1 ? xO (x = 0.02) thin film, which indicates the highly promising candidate for use in optoelectronic devices.  相似文献   

15.
In this work, we present a systematic study on the effect of monovalent and divalent cation inclusion on the magnetic properties of the manganites series La0.80(Ag1?xSrx)0.20MnO3 (x = 0.0–1.0) synthesized by the solid‐state reaction method. The decreasing Sr:Ag proportion across the compositional series was verified by X‐ray photoelectron spectroscopy. Concerning magnetic properties, the hysteresis curves manifested an initial paramagnetic response at x = 0.0, followed by a progressive ferromagnetic behavior with an optimum Ag:Sr ratio at x = 0.75, for which an enhanced saturation magnetization of 51 Am2/kg and a Curie temperature of 336 K were recorded. Results are explained on the basis of the effect of the increasing unit cell volume on the double exchange interaction between magnetic Mn3+– Mn4+ atoms.  相似文献   

16.
Evolution of crystal structure in Pb1‐xBax(Fe1/2Nb1/2)O3 ceramics has been investigated by X‐ray diffraction and Raman spectra analysis together with the dielectric characterization. The crystal structure for all compositions is cubic and the cell volume indicates a sudden change at = 0.075. Pb1‐xBax(Fe1/2Nb1/2)O3 ceramics with > 0.075 are paraelectric, whereas those for < 0.075 are ferroelectric at room temperature. The evolution of phonon modes indicates that the ferroelectricity of Pb1‐xBax(Fe1/2Nb1/2)O3 solid solution ceramics is caused by the off‐center Nb5+ in BO6 octahedron. The ferroelectric‐related distortion is still observed in paraelectric solid solutions with > 0.075.  相似文献   

17.
(ZrO2)1–x(Yb2O3)x binary systems were investigated in the doping range of 0.02 ≤  0.12. Ytterbium‐doped zirconia powders were synthesized using the Pechini method. X‐ray diffraction (XRD) measurements showed that fcc ZrO2 was stabilized for 8–12 mol% Yb‐doping rate. The produced Yb‐stabilized Zr (YbSZ) films were characterized; their thickness and homogeneity properties depended on the nature of the YbSZ slurry. All coating parameters were optimized and determined with precoating treatments. The samples were characterized by differential thermal analysis/thermal gravimetry (DTA/TG), scanning electron microscopy (SEM) and ac impedance measurements.  相似文献   

18.
Single‐phase monoclinic aluminum–gallium oxide powders, β?(AlxGa1?x)2O3, have been produced by solution combustion synthesis for Al fraction 0 ≤ x < 0.8. α?(AlxGa1?x)2O3 is observed for x = 1, with mixed α + β for x = 0.8. The contraction in lattice parameters and increase in band gap with increasing Al concentration were characterized by X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS), respectively, and are compared with a first‐principles density‐functional theory calculation. A novel filtering procedure is described to reduce the uncertainty involved in measuring band gap using photoemission, and to remove asymmetry in XPS line shapes caused by differential charging of loose powder. The lattice parameters vary linearly with Al fraction, but exhibit a change in slope at x = 0.5 that is attributed to the difference between aluminum occupying tetrahedral and octahedral sites in the monoclinic lattice. The band gap changes linearly with local stoichiometry, including increasing when aluminum content at the surface is enriched relative to the interior, with a range of over 1.8 eV.  相似文献   

19.
GeTe is a medium-temperature thermoelectric material with excellent performance. The thermoelectric performance of GeTe is affected by the carrier concentration generated by Ge vacancy. Therefore, it is of important to study the effect of excess Ge or Te on the thermoelectric performance of GeTe. In this paper, GexTey materials (x:y = 1:1.08, 1:1.06, 1:1.04, 1:1, 1.05:1, 1.075:1, and 1.1:1) were fabricated by high-pressure sintering (HPS) and spark plasma sintering (SPS), respectively, to study the effects of different Ge/Te atomic ratios and preparation process on the thermoelectric properties of polycrystalline GeTe. The composition and microstructure were investigated by an X-ray diffraction method (XRD) and field-emission scanning electron microscope (FESEM). The thermoelectric performance was tested from 303 to 703 K. The measurement results show that the Seebeck coefficient of GexTey increases and the conductivity decreases with the decreasing in Te content or the increasing in Ge content. Ge1Te1 exhibits the highest power factor because its Seebeck coefficient and conductivity are at an average level. Owing to the presence of pure Ge and the decrease of Ge vacancy, the lattice thermal conductivities of samples with excess Ge are higher than that of Ge1Te1. Ge1Te1 sintered by HPS has the highest ZTmax value, reaching 1.37 at 723 K.  相似文献   

20.
Chromium copper (Cr Cu) catalysts are well‐known burning rate catalysts for solid propellants, which were used as energy source for rocket propulsion [1]. The present work reports the enhancement of lithium perchlorate (LiClO4) by employing copper chromium as a catalyst. The LiClO4 decomposition rate depends on the catalyst characteristics, such as chemical composition, specific surface, and crystalline structure. Scanning electron microscopy, Brunauer‐Emmett‐Teller, X‐ray diffraction, X‐ray photoelectron spectroscopy, and H2‐temperature‐programmed reduction analyses were used to characterize CrxCu(1−x)O(1+0.5x) catalysts. The samples are prepared using the sol‐gel method with different mole ratios. Furthermore, the samples are tested to evaluate their effect on the LiClO4 decomposition at various temperatures. The blank tests comparison shows that the CrxCu(1−x)O(1+0.5x) catalysts strongly enhance the LiClO4 decomposition. Moreover, CuCr2O4 is formed in the CrxCu(1−x)O(1+0.5x) catalysts. The Cr Cu binary composite catalysts show smaller crystallites, larger surface area, and better catalytic performance than the pure CuO samples because of the interaction of Cr and Cu ions. This study proposes a hypothetical reaction mechanism for the LiClO4 catalytic decomposition of the CrxCu(1−x)O(1+0.5x) catalysts.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号