Determined Lattice Parameters Research Articles

Crystal structure, Chemical Bonding, and Magnetism of α-Fe6Ga5: How Local Interactions Shape the Structure and Properties of Intermetallic Compounds.

α-Fe6Ga5 was synthesized from the elements as a polycrystalline powder. Its crystal structure was redetermined by high-resolution powder X-ray diffraction, which showed a complex monoclinic structure of the Fe6Ge5 type. The determined lattice parameters (a = 10.08380(6) Å, b = 7.97071(5) Å, c = 7.70489(5) Å, and β = 108.3062(2)°) differ notably from the previous reports. Despite possessing the same structure type as Fe6Ge5, α-Fe6Ga5 displays several distinctive features, such as short Ga-Ga bonds and distorted Fe layers. According to magnetization measurements, α-Fe6Ga5 is a soft ferromagnet with a high Curie temperature of 760 K, which is in stark contrast to the antiferromagnetic behavior of Fe6Ge5 reported in the literature. The electronic structure of α-Fe6Ga5 was studied theoretically using density functional theory-calculations, which showed the pronouncedly covalent character of the short Fe-Ga and Ga-Ga bonds. Similar calculations were performed for Fe6Ge5, which revealed stronger Fe-Ge interactions, which preclude the formation of short Ge-Ge bonds. In both cases, the theoretical calculations showed ferromagnetic instability, which leads to ferromagnetic ordering only in the case of α-Fe6Ga5, likely due to the different nature of Fe-Ga-Fe and Fe-Ge-Fe superexchange interactions.

Pressure action on ductility and optoelectronic properties of non-toxic AGeBr[formula omitted] (A = Cs, K, Na, Rb) perovskites

We performed first-principles calculations base on generalized gradient approximation(GGA) in the framework of density functional theory (DFT) to examine the effect of pressure on the structural, mechanical, electronic and optical properties of non-toxic AGeBr3 perovskites (A = Cs, K, Na, Rb) for applications in photovoltaic and optoelectronic devices. The dependence of physical properties is evaluated for several pressure values ranging from 0 GPa to 10 GPa. The determined lattice parameters show agreement with previous values and decrease with the applied pressure. All considered materials show semiconductor behavior with direct bandgap (R ⟶ R) at atmospheric pressure. The hybrid functionals HSE and PBE0 have been used to determine accurate values for bandgaps. A very good agreement was found with available experimental values. The calculated bandgap values were found to be 2.129 [2.608] for CsGeBr3, 2.065 [2.481] for KGeBr3, 2.032 [2.397] for NaGeBr3 and 2.089 [2.530] for RbGeBr3, at the HSE [PBE0] level of theory. However, as the applied pressure increases, a reduction in the bandgap is observed, leading to semiconductor to metallic transition. The materials similarly show improved optical properties under pressure with high absorption coefficients in the visible and ultraviolet regions. In addition, the ductility and stability of the considered materials were found also to improve under hydrostatic pressure, which makes them suitable for incorporation into thin films for high performance optoelectronic devices application.

First-principles calculations to investigate the physical properties of lead-free double perovskites Cs2AgXCl6 (X=P, Co, As, Cd) for optoelectronic applications

In this work, we have been systematically studied the structural, electronic, optical, mechanical, and thermodynamic properties of double perovskite Cs2AgXCl6 (X= P, Co, As, Cd) by adopting first-principles calculations based on density functional theory (DFT). We found that the determined lattice parameters are in good agreement with the previously reported study, which are 7.518558 Å, 7.491051 Å, 7.370192 Å, and 7.517199 Å for Cs2AgAsCl6, Cs2AgCdCl6, Cs2AgCoCl6, and Cs2AgPCl6, respectively. The negative result of formation energy (ΔHf) indicates that these compounds are thermodynamically stable and can be experimentally synthesized. The electronic energy band structure indicates that Cs2AgXCl6 (X=P, Co, As, Cd) compounds are semiconductor behavior with the band gap (Eg) of 1.047 eV, 1.085 eV, 1.205 eV, and 2.074 eV for Cs2AgPCl6, Cs2AgCoCl6, Cs2AgAsCl6, and Cs2AgCdCl6, respectively. Electronic properties suggest that carrier transport is enhanced in Cs2AgXCl6 (X=P, Co, As, Cd) because of holes and electrons' small effective mass. Furthermore, optical properties suggest that these compounds have high absorption coefficients and low reflectivity values in the visible region. The structural and thermodynamic stability, the obtained energy band gap, tunable optical properties, and interesting thermodynamic properties indicate that Cs2AgXCl6 (X=P, Co, As, Cd) is a potential candidate in photovoltaic and optoelectronic applications.

Ce2Pd21Si6 vs. Ce3Pd20Si6: Effect of Ce/Pd substitution on the physical properties

In this study, polycrystalline intermetallic compounds Ce3-xPd20+xSi6 (x = 0; 0.5; 1) as well as La-based analogues La3-xPd20+xSi6 (x = 0; 1) are synthesized. At the same time, R2Pd21Si6 (RCe, La) are new rare earth compounds presented here. An analysis of the crystal structure shows that the increase in x leads to partial (x = 0.5) or complete (x = 1) replacement of Ce/La ions by Pd in one of the two Wyckoff positions, namely, in position 4a. Ab initio DFT calculations demonstrate good agreement between the determined lattice parameters and those found experimentally for both Ce3-xPd20+xSi6 (x = 0; 0.5; 1) and La3-xPd20+xSi6 (x = 0; 1). A comparative analysis of resistivity and specific heat of Ce3-xPd20+xSi6 with x = 0; 0.5; 1 makes it possible to associate the Ce ions in the 8c position with Kondo behaviour in all three compositions, which manifests itself in an increase in resistivity with cooling, as well as in a broad peak of the magnetic contribution of specific heat. The Kondo temperature TK ≈ 25 K obtained from the analysis of the temperature dependences of the heat capacity turns out to be the same for all Ce compounds. The appearance of cerium ions in the position 4a in compositions with х = 0 and х = 0.5 leads to an additional contribution to the specific heat, the value of which increases with decreasing temperature, as well as, to the formation of a coherent Kondo-lattice state with a maximum of the resistivity at Tcoh ≈ 15 K, followed by the subsequent onset of negative magnetoresistance regime below Tinv≈ 7 K. Apparently, this behaviour is associated with the appearance of spin and orbital correlations proceeding the quadrupole and antiferromagnetic transitions occurring at lower temperatures. Magnetization measurements show more localized character of magnetic moments of Ce ions at T = 2 K in Ce3Pd20Si6 as compared to the Ce2Pd21Si6.

Insights into the physical properties of inverse-Heusler alloy Cr2CoGa via density functional theory

First-principles analyses are accomplished on the structural, mechanical, thermal, electronic, and optical properties of inverse-Heusler alloy Cr2CoGa using density functional theory. Our determined lattice parameters agree very well with prior findings. The mechanical properties of both cubic and tetragonal phases of Cr2CoGa compound are thoroughly investigated. The elastic constants meet the Born criteria for mechanical stability of the studied compound. The ductile behavior is exhibited by the calculated Pugh’s ratio 2.66 and 2.91 as well as the Poisson’s ratio 0.33 and 0.35 for cubic and tetragonal phase, respectively, and the tetragonal phase is more ductile comparing this two phases. The universal elastic anisotropy of cubic and tetragonal Cr2CoGa is 0.25 and 0.28, respectively, revealing their anisotropic nature, which is also confirmed by the non-spherical 3D anisotropy contour plots. The estimated Debye temperature and minimum thermal conductivity suggest potential application of Cr2CoGa as a thermal barrier coating. The calculated electronic band structure and density of states suggest the metallic characteristics of Cr2CoGa. Moreover, the important optical parameters, namely, dielectric constants, refractive index, absorption coefficient, photoconductivity, reflectivity, and loss function are also investigated and discussed towards the efficient applications of Cr2CoGa.

Structure, growth and characterization of a new naphthalene family crystal for fluorescence and third order nonlinear optical applications

In the present work we have investigated the fluorescence and nonlinear optical property of a new naphthalene family crystal, Decyl 6-(decyloxy)naphthalene-2-carboxylate (D6DN2C). This crystal was grown for the first time by slow evaporation solution technique (SEST). Single crystal X-ray diffraction analysis reveals that D6DN2C belongs to triclinic crystal system with centrosymmetric space group of Pī. The determined lattice parameters are a = 8.669 (3) Å, b = 9.495 (3) Å, c = 19.757 (6) Å, α = 82.697 (1)°, β = 77.726 (1)°, γ = 65.465 (1)°and volume = 1444.17 (8)Å3. Functional groups present in D6DN2C were identified by FT-IR studies. Transparency of the title crystal in UV–Visible region was analyzed and the optical band gap energy was found to be 3.51eV.Fluorescence spectra were recorded for the excitation wavelength of 300 nm. The negative third order nonlinear optical parameters like refractive index (n2), absorption coefficient (β) and susceptibility (χ(3)) were estimated by Z-scan studies.

Synthesis of binary Co–Mg–O oxide system and study of its behavior in reduction/oxidation cycling

The nanoscale Co–Mg–O oxide sample (15 wt% in terms of Co3O4) was prepared from the corresponding xerogel synthesized by the modified sol-gel method. The hydrolysis of as-prepared Mg(OCH3)2 was carried out using the aqueous solution of Co(NO3)2 precursor. The CoOx nanocrystallites of about 10–20 nm in size were shown to be uniformly distributed within the MgO matrix. The reduction of Co–Mg–O in H2 flow was found to proceed in two separate stages within the temperature ranges of 200–350 °C and 350–600 °C. The prepared binary Co–Mg–O system was demonstrated to possess completely reproducible reduction behavior in the consecutive reduction/reoxidation cycles. The phase composition of the sample exposed to both the reducing and oxidative environment was followed by an in situ X-ray diffraction analysis performed at temperatures of 25, 300, 500 and 700 °C. The determined lattice parameters for MgO (a = 4.219 Å) and Co3O4 (a = 8.110 Å) were found to be slightly increased as compared with the values from Powder Diffraction File, so that the formation of joint non-stoichiometric (Mg1-xCox)O and (Co3-xMgx)O4 phases was suggested. The strong chemical interaction of cobalt oxide with MgO matrix was also evidenced by the data of a diffuse reflectance UV–vis spectroscopy.

Synthesis of manganese sulfide (MnS) thin films by chemical bath deposition and their characterization

Films of γ-MnS were deposited by chemical bath deposition (CBD) technique on glass slide substrates. The EDAX analysis showed that the film contains Mn and S elements without any other impurity. The EDAX weight percentage showed the film to be in perfect stoichiometry. The XRD showed that the synthesized MnS thin film possess hexagonal structure. The determined lattice parameters a=b=3.9Å and c=6.4Å were in match with the reported values. The crystallite size determined using XRD pattern employing Scherrer's formula and Hall–Williamson plot were 8.35nm and 7.42nm, respectively. The SAED shows ring pattern, clearly stating the thin film to be polycrystalline in nature. The SEM image of MnS thin film clearly reveals that the film surface is homogenous consisting of two sizes of spheres. Smaller spherical grain particles of size ∼1.6–2μm covers the substrate and on top of covered small grain size particles are the large size spherical grain particles having size ∼5.0–7.0μm. The 2D AFM image of MnS thin film shows coalescences between spherical grains. The optical absorbance analysis of the MnS thin film confirmed that the film possesses direct and indirect optical bandgap values of 3.67eV and 2.67eV, respectively. All the obtained results have been deliberated in this paper.

Synthesis, growth and characterization of new organic crystal: 2-Aminopyridinium p-Toluenesulfonate for third order nonlinear optical applications

2-Aminopyridinium p-Toluenesulfonate (2APPTS), an organic NLO crystal, was grown for the first time by the slow evaporation solution technique. Single crystal X-ray diffraction analysis reveals that 2APPTS belongs to monoclinic crystal system with centrosymmetric space group P21/n. The determined lattice parameters are a=8.580(7)Å, b=6.419(5)Å, c=23.277(18)Å, β=100.016(3)° and volume=1262.58(3)Å3. Powder XRD study reveals the crystalline nature of the grown sample. FT-IR and FT-Raman studies were carried out to identify the functional groups present in 2APPTS. FT-NMR spectral study confirms the number of protons and carbon present in the molecular structure of the title compound. Thermal behavior and stability of 2APPTS were investigated by thermogravimetric (TG) and differential thermal analyses (DTA). Transparency of the title crystal in UV–vis–NIR region was analyzed and the optical band gap energy was found to be 3.6eV. The mechanical properties of the grown crystals have been analyzed by the Vickers microhardness method. The etching studies reveal the growth pattern and dislocations present in the grown 2APPTS crystal. The negative third order nonlinear optical parameters like refractive index (n2), absorption coefficient (β) and susceptibility (χ(3)) were estimated by Z-scan studies.

Sulfidiodide (MSI) der schweren Lanthanoide (M = Gd – Lu): Kristallstrukturen und magnetische Eigenschaften

AbstractFrom reactions of equimolar quantities of the heavier lanthanoids (M = Gd – Lu) with the elements sulfur and iodine in fused silica ampoules (900 °C, 10 d) phase‐pure samples of the lanthanoid sulfide iodides MSI (M = Gd – Lu) could be prepared. Besides the already structurally determined sulfide iodides MSI with M = Gd and Dy, all samples could be characterized by means of X‐ray powder diffraction and their magnetic behavior was examined. In addition a single‐crystal structure refinement for HoSI was carried out (orthorhombic, Pmmn; a = 415.09(4) pm, b = 531.34(5) pm, c = 920.53(9) pm), which confirmed the isotypy of the later lanthanoid sulfide iodides with the structure of FeOCl. On the basis of the X‐ray powder diffraction experiments all prepared compounds could be indexed in a primitive orthorhombic unit cell. An analysis of the determined lattice parameters and cell volumes resulted in the typical lanthanoid contraction for compounds within the row of the 4f elements. The magnetochemical studies led to the expected effective magnetic moments for trivalent lanthanoid cations without showing any magnetic ordering phenomenon.

Use of EBSD to study electropulsing induced reverse phase transformations in a Zn-Al alloy (ZA22)

Multi-phase identification and phase transformations in electropulsing treated Zn-Al based alloy wire specimens were studied using electron back-scattered diffraction, back-scattered scanning electron microscopy and X-ray diffraction techniques. By using electron back-scattered diffraction, two phases: η'(S) and η'(T) with a small difference of about 1% in lattice parameters (c(0)/a(0) ) were identified, based on the determined lattice parameters of the phases, and the reverse eutectoid phase transformations: η'(T) +ɛ'(T) +α'(T) →η'(S) and ɛ+α→T'+η were successfully detected. Electron back-scattered diffraction appeared to be an effective technique for studying complex electropulsing induced phase transformations.

Preparation and characterization of flash-evaporated CuInSe 2/CuGaSe 2 thin films

Deposition of CuInSe 2 thin film on CuGaSe 2 thin film (CuInSe 2/CuGaSe 2) has been prepared by flash evaporation technique on Corning glass substrates heated at T s = 250 °C and annealed at 450 °C in an argon atmosphere. The properties of the resulting films have been examined by scanning electron microscopy (SEM) and X-ray diffraction. The optical measurements have been carried out in the wavelength range 500–3000 nm. X-ray diffraction revealed that the film was single-phase with chalcopyrite structure and has a preferred orientation along the (1 1 2) plane. The determined lattice parameters were a = 5.75 Å and c = 11.56 Å. SEM micrographs revealed grain sizes ranging from 0.03 μm to 0.04 μm. The thickness of the thin films is around 0.8 μm. The absorption coefficient of this film was above 2.25 × 10 4 cm −1 and the band gap was found to be 1.14 eV. The annealing in Ar did not influence the composition of the layers considerably but improved the crystalline structure quality.

Synthesis, Characterization, and X-ray Diffraction Studies of Co(II), Ni(II), and Cu(II) Tellurite (TeO3 2 −) Complexes with Nicotinic Acid

A series of complexes of the type H x [M 2+ (NA) n TeO 3 ].YH 2 O [Where M(II) = Co(II), Ni(II) and Cu(II), X = 2, n = 3 and Y = 6 for Co(II) and Ni(II); X = l, n = 2 and Y = 3 for Cu(II); NA = Nicotinic acid] have been synthesized, and characterization of the ligand, as well as complexes, has been done on the basis of elemental analysis, conductivity, magnetic susceptibility measurements, spectral studies. Thermogravimetric analysis and XRD studies, various ligand field parameters like Dq, B,β, etc. have been evaluated for Co(II) and Ni(II) complexes, which suggests an octahedral geometry for the complexes and square planar structure for Cu(II) complex. x-ray diffraction studies have been undertaken to determined lattice parameters viz. crystal system, crystal lattice edge, etc.

A new method of strain determination in partially relaxed thin films

AbstractIt is well known that classical Stoney's formula for radius of thin film bowing fails when thin film is dislocated. Thereby, a method of determination lattice parameters for each of heterostructure epilayers is needed when inelastic relaxation takes place. In this article, we have developed a method of determination lattice parameters of a heterostructure from radius curvature measurement data. Description of deformation when dislocations are nucleated is carefully analyzed. It is shown that in order to take into account nucleated dislocations in thin film an additional term responsible for increased volume of layers should be included in the analysis. The proposed method is based on the finite deformation elasticity and uses the finite element method and bowing radius measurement by the laser beam reflection method. As an example the nitride alloy heterostructure with GaN as a substrate is analyzed. The verification is performed using X‐ray measurement of lattice parameters. A very good correspondence between numerically determined lattice parameters and XRD measurements data are observed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Solvent-free synthesis of crystalline carbon nitride compounds

A carbon nitride sample has been successfully synthesized by a chemical reaction between 1,3,5-trichlorotriazine and ammonium chloride at a temperature of 400 °C without any solvent. Through the measurements of X-ray diffraction, transmission electron microscopy (TEM) and electron energy loss spectroscopy, it is convinced that a polycrystalline graphitic carbon nitride phase has been synthesized in the sample. Its determined lattice parameters of a and c are 4.65 Å and 6.48 Å. In addition to the dominant graphitic carbon nitride phase, another structured carbon nitride phase is also observed in TEM. Its determined d values from selected area electron diffraction pattern are in good agreement with the theoretical calculation results of α-C 3N 4, implying that α-C 3N 4 be possibly formed in the obtained sample.

Preparation of chalcopyrite-type CuInSe 2 by non-heating process

Chalcopyrite-type CuInSe 2 was successfully prepared by using mechanical alloying (MA) method. Various process parameters such as reaction system, rotational speed and milling period were investigated in detail. The determined best condition for the preparation of CuInSe 2 was that the reaction system was Cu+In+2Se→CuInSe 2, the rotational speed was 250 rpm and the milling period was 60 min. In the X-ray diffraction pattern of the CuInSe 2 sample prepared by the MA, characteristic peaks of the chalcopyrite-type structure such as 1 0 1, 2 1 1 and 3 1 1 were clearly observed. The determined lattice parameters were a=5.7759(1) Å and c=11.5950(1) Å ( c/ a=2.007). The crystallographic structure of the CuInSe 2 sample was analyzed by Rietveld analysis using X-ray powder diffraction data.

Subsolidus phase relations in the SnO2–CuSb2O6 binary system

Abstract The SnO 2 –CuSb 2 O 6 binary system plays a significant role in the SnO 2 –Sb 2 O 3 –CuO ternary system, delimiting the compositional ranges and their sensor and catalytic properties. The initial compositions expressed as (1− x ) SnO 2 – x CuSb 2 O 6 were treated both non-isothermally using DTA up to 1500 °C and iso-thermally at temperatures between 1000 and 1200 °C. Phase analysis of the samples was determined by XRD and IR spectroscopy. It was established that SnO 2 –CuSb 2 O 6 is a pseudobinary system with a solid solubility limit of the end members. The determined lattice parameters of the unit cell of the obtained rutile and trirutile solid solutions obeyed Vegard's rule. From IR spectral investigations it was inferred that Sn 4+ might be preferentially incorporated on Sb 5+ sites into the CuSb 2 O 6 lattice.