The chemical state of transition element cations in oxide pyrochlore Bi2Cu1/2Ni1/2Ta2O9+delta (sp. gr. Fd-3m, a=10.5378(6)angstrom) synthesized by the solid-phase method was studied using X-ray absorption spectroscopy (NEXAFS, XPS). The parameters of the XPS spectra of Bi4f, Ta4f, Ta5p, Ni2p, Cu2p for multielement pyrochlore are compared with the parameters of transition element oxides. A characteristic shift of the Ta4f spectrum to lower energies by 0.7 eV is observed for pyrochlore, due to which the effective charge of tantalum cations is +(5-delta). It is shown that the NEXAFS Cu2p spectra of oxide ceramics, according to the main characteristics of the spectrum, represent a superposition of the spectra from the Cu(I) and Cu(II) cations. Based on the analysis of the relative intensity of peaks in the XPS spectrum of Cu2p for pyrochlore, the content of cations Cu(I)/Cu(II)=2/3 was estimated. According to the nature of the NEXAFS and XPS Ni2p spectra, nickel ions are in the state of Ni(II,III).

Bi2ZnxMn1–xTa2O9.5–∆ ceramics were synthesized for the first time using the solid phase synthesis method. The samples were found to contain cubic pyrochlore (sp. gr. Fd–3m) as the main phase and a triclinic modification (sp. gr. P-1) of BiTaO4 as admixture. The amount of the triclinic modification is proportional to the manganese content in the samples. The formation of impurities is associated with the distribution of a fraction of the transition element ions into the cationic sublattice of bismuth (III). The unit cell parameter of the pyrochlore phase increases with increasing content of zinc ions in the samples from 10.4895(5) Å (x = 0.3) to 10.5325(5) Å (x = 0.7) in accordance with the Vegard rule. The formation of impurities in samples can be prevented by creating a bismuth ion deficiency in the bismuth sublattice by an amount proportional to the β-BiTaO4 content. The unit cell parameter of single-phase pyrochlores Bi2–yZnxMn1–xTa2O9.5–∆ synthesized in this way increases with increasing zinc ion content in the samples from 10.4764(5) Å (x = 0.3) to 10.5122(5) Å (x = 0.7). As observed through electron scanning microscopy, the ceramic samples exhibit a low-porosity microstructure with indistinct grain boundary outlines. The porosity of the samples decreases as the zinc content of the samples increases. The formation of a deficient bismuth sublattice during preparation is associated with a more porous microstructure, which can be attributed to a reduced concentration of the readily fusible component present in the reaction mixture, namely bismuth (III) oxide.

The concentration interval for the formation of phase-pure zinc- containing pyrochlores based on bismuth tantalate was established. It was shown that for the Bi-2+& khcy;(+3)(Zn2/3Ta4/3)O-+8(7-& ucy;) and Bi1.65Zn1+xTa2-xO9 series, single- phase samples are formed at 1.575 <= x(Bi) <= 1.725 and 0.90 <= x(Zn) <= 1.14. The cubic unit cell parameter (space group Fd -3m) for the first and second series of samples increases from 10.5295(5) to 10.5486(5) & Aring; and from 10.5310(5) to 10.5435(5) & Aring;, respectively, following the Wegard rule. It was shown that a significant part of Zn(II) ions is located in the bismuth position. In all cases phase-pure pyrochlores are formed in the case of bismuth deficiency in the bismuth sublattice by 42.5-47.5 at.% for Bi-2+& khcy;(+3)(Zn2/3Ta4/3)O-+8(7-& ucy;), and the filling degree of the octahedral sublattice of Ta(V) with bismuth ions is limited to 30-38 %. It was found that the deficit of bismuth ions in the bismuth sublattice depends on the amount of zinc in the samples with the more zinc in the samples, the less vacancy of the bismuth sublattice. The inclusion of pyrochlore with Bi3/2ZnTa3/2O9 ideal composition in the composite pyrochlore region and the exclusion of the Bi2Zn2/3Ta4/3O7 monoclinic zirconolite-like phase are confirmed. It was shown that low-porosity sintered samples are formed, while the porosity of ceramics decreases with increasing molar ratio of n(Bi)/n(Ta) and the amount of zinc in the samples

Pyrochlore Bi1.8Mn0.5Ni0.5Ta2O9-Δ (sp.gr. Fd-3m, a = 10.5038(9) Å) was synthesized by the solid-phase reaction method and characterized by vibrational and X-ray spectroscopy. According to scanning electron microscopy, the ceramics are characterized by a porous microstructure formed by randomly oriented oblong grains. The average crystallite size determined by X-ray diffraction is 65 nm. The charge state of transition element cations in the pyrochlore was analyzed by soft X-ray spectroscopy using synchrotron radiation. For mixed pyrochlore, a characteristic shift of Bi4f and Ta4f and Ta5p spectra to the region of lower energies by 0.25 and 0.90 eV is observed compared to the binding energy in Bi2O3 and Ta2O5 oxides. XPS Mn2p spectrum of pyrochlore has an intermediate energy position compared to the binding energy in MnO and Mn2O3, which indicates a mixed charge state of manganese (II, III) cations. Judging by the nature of the Ni2p spectrum of the complex oxide, nickel ions are in the charge state of +(2+ζ). The relative permittivity of the sample in a wide temperature (up to 350 °C) and frequency range (25–106 Hz) does not depend on the frequency and exhibits a constant low value of 25. The minimum value of 4 × 10−3 dielectric loss tangent is exhibited by the sample at a frequency of 106 Hz. The activation energy of conductivity is 0.7 eV. The electrical behavior of the sample is modeled by an equivalent circuit containing a Warburg diffusion element.

Phase-pure pyrochlore with the composition Bi1.62Cr1/2Cu1/2Ta2O9+Delta (space group Fd-3m, a = 10.4537(8) & Aring;) was synthesized using the solid-phase synthesis method. The sample is characterized by a porous microstructure formed by partially fused crystallites with an average longitudinal size of 1-2 mu m. The charge state of transition element cations in oxide ceramics was studied using ultrasoft X-ray spectroscopy using synchrotron radiation (NEXAFS, XPS). The energy position of the XPS Bi4f, Bi5d and Ta4f, Ta5p spectra is shifted towards lower energies compared to the binding energy in tantalum(V) and bismuth(III) oxides by 0.2 and 0.8, respectively. Bismuth and tantalum cations have the same effective charge + (3-delta) and + (5-delta). The NEXAFS Cr2p spectrum of ceramics, according to the main characteristics of the spectrum, practically coincides with the spectrum of Cr2O3 and indicates the content of chromium ions in the oxide ceramics in the form of Cr(III), and according to the nature of the Cu2p spectrum, copper ions are predominantly in the Cu(II) state. The sample exhibits semiconductor properties. At 25 degrees & Scy;, the relative dielectric permittivity of the sample at 106 Hz is 37, dielectric losses are minimal and amount to 3 & sdot;10- 2. The activation energy for conductivity is 0.40 eV. The electrical behavior of the sample is modeled by equivalent electrical circuits. It is shown that upon heating, the rate of charge transfer processes in the sample increases, and the polarization inhomogeneity of the sample decreases.

Complex antimony pyrochlores Bi2.7M0.46Ni0.70Sb2O10+Δ (M = Zn, Mg) were synthesized from oxide precursors, using the solid-state reaction method. For each composition variant, the pyrochlore phase formation process was studied during solid-state synthesis in the range of 500–1050 °C. The influence of zinc and magnesium on the phase formation process was established. The interaction of oxide precursors occurs at a temperature of 600 °C and higher, resulting in the formation of bismuth stibate (Bi3SbO7) as a binary impurity phase. Oxide precursors, including bismuth(III) and antimony(III,V) oxides, are fixed in the samples up to 750 °C, at which point the intermediate cubic phase Bi3M2/3Sb7/3O11 (sp. gr. Pn-3, M = Zn, Ni) is formed in the zinc system. Interacting with transition element oxides, it is transformed into pyrochlore. An intermediate phase with the Bi4.66Ca1.09VO10.5 structure (sp. gr. Pnnm) was found in the magnesium system. The unit cell parameter of pyrochlore for two samples has a minimum value at 800 °C, which is associated with the onset of high-temperature synthesis of pyrochlore. The synthesis of phase-pure pyrochlores is confirmed by high-resolution Raman spectroscopy. The data interpretation showed that the cations in Ni/Zn pyrochlore are more likely to be incorporated into bismuth positions than in Ni/Mg pyrochlore. The nickel–magnesium pyrochlore is characterized by a low-porosity microstructure, with grain sizes of up to 3 μm, according to SEM data. Zinc oxide has a sintering effect on ceramics. Therefore, the grain size in ceramics is large and varies from 2 to 7 μm.

Using the Pechini method, a phase-pure and highly dispersed complex oxide Bi2Ni0.5 & Scy;o(0.5)Ta(2)O(9+Delta)(space group Fd-3m, a=10.5348(5) & Aring;) with a pyrochlore structure was synthesized. At a synthesis temperature of 1050 degrees C, highly porous ceramics are formed with an average crystallite grain size of 41 nm according to X-ray diffraction data. The results of elemental mapping indicate a uniform distribution of atoms of transition elements in the sample, and X-ray energy dispersive analysis showed that the chemical composition of the synthesized sample corresponded to the specified theoretical composition. The formation of the pyrochlore phase proceeds through the formation of of an intermediate phase-bismuth orthotantalate of the orthorhombic modification, the content of which decreases with increasing heat treatment temperature from 16 (850 degrees C) to 2 mol.% (950 degrees C).

This paper reports results from a study of two new genetic types of diamond discovered in Kamchatka. These diamonds were formed under extra-mantle conditions, as can be inferred from the fact that there is no indication of post-crystallization annealing with the formation of aggregated nitrogen defects in them. The first of these types is defined by us as volcanic-atmoelectrogenic. This is formed directly in a volcanic ash-gas cloud due to deep-seated methane released by atmospheric electric discharges. The second genetic type of diamonds is formed at depth within a magmatic-pneumatolytic-hydrothermal ore deposit, and can be defined as the explosive-tuffisite type. The industrial potential of these types enables us to assert the discovery of a new diamondiferous province, i.e., the Kamchatka Province.

Co doped bismuth magnesium tantalate with a pyrochlore structure (sp. gr. Fd-3m) was synthesized for the first time using the standard ceramic method. Single phase Bi2Mg1−xCoxTa2O9 samples were found to be formed when x < 0.7 in the X-ray phase analysis. However, with a higher cobalt content in the samples, the impurity phase β-BiTaO4 (sp. gr. P-1) is detected, and its amount is proportional to the degree of cobalt doping. The formation of solid solutions is evidenced by a uniform increase in the unit cell parameter of the Co,Mg co doped bismuth tantalate phase with an increase in the content of cobalt ions in the samples from 10.5412(8) (x = 0.3) to 10.5499(8) Å (x = 0.7). The samples exhibit a porous microstructure consisting of chaotically oriented and partially fused elongated grains measuring 1–2 μm. The dependence of the ceramic grain size on the n(Mg)/n(Co) ratio was not determined. X-ray spectroscopy (ear dge X-ray bsorption ine tructure (NEXAFS) and X-ray photoelectron spectroscopy (XPS)) was used to study the charge state of ions in Bi2Mg1−xCoxTa2O9. The NEXAFS and XPS data showed that doping with cobalt and magnesium did not change the bismuth and tantalum oxidation states in pyrochlore; in particular, the ions maintained their oxidation states of Bi(+3), Mg(+2) and Ta(+5). The energy position of the peaks of the Ta4f-, Ta5p-, Ta4d spectra had a characteristic shift towards lower energies compared to the binding energy in pentavalent tantalum oxide Ta2O5. A shift towards lower energies is characteristic of a decrease in the effective positive charge; in particular, for the Ta4f and Ta4d spectra we presented, this energy shift was ΔE = 0.65 eV, and in the region of the Ta4d edge—0.55 eV. This in turn allowed for us to assume that tantalum atoms have the same effective charge +(5-δ). The oxidation state of cobalt ions was predominantly 2+ and partially 3+, according to NEXAFS spectroscopy data.

Mixed copper-containing pyrochlores Bi 2 Co 1/2 Cu 1/2 Ta 2 O 9 +Delta , Bi 2 Ni 1/2 Cu 1/2 Ta 2 O 9 +Delta , Bi 2 Co 1/3 Cu 1/3 Ni 1/3 Ta 2 O 9 +Delta (sp.gr. Fd-3 m ) were synthesized by the solid-phase reaction method. The surface composition and chemical state of transition element atoms in pyrochlores were characterized by XPS, NEXAFS spectroscopy. According to the XPS spectra, bismuth and tantalum cations have an effective charge of + 3 and +(5- delta ). The NEXAFS Cu2p spectra of pyrochlores are shown to represent a superposition with the CuO and Cu2O 2 O spectra in terms of the main spectral characteristics. This indicates a variable Cu ion content in oxide pyrochlores in the form of Cu(I,II) ions.

Two series of the bismuth tantalate pyrochlore samples, codoped with Mg,Mn and Zn,Mn, were synthesized via solid-phase reaction. It was established that the Bi2Mg(Zn)xMn1−xTa2O9.5−Δ (x = 0.3; 0.5; 0.7) samples contain the main phase of cubic pyrochlore (sp. gr. Fd-3m) and an admixture of triclinic BiTaO4 (sp. gr. P-1). In both sets, the amount of BiTaO4 is proportional to the amount of manganese doping, however, zinc-containing samples have a higher level of impurities than magnesium-containing ones. The unit cell parameter of the Zn,Mn codoped bismuth tantalate phase increases with an increasing content of zinc ions in the samples from 10.4895(5) (x = 0.3) to 10.5325(5) Å (x = 0.7). The unit cell parameter of Mg,Mn codoped bismuth tantalate pyrochlores increases uniformly with an increasing index x(Mg) from 10.4970(8) at x = 0.3 to 10.5248(8) Å at x = 0.7, according to the Vegard rule. The NEXAFS and XPS data showed that the ions were found to have oxidation states of Bi(+3), Ta(+5), Zn(+2) and Mg(+2). In the Ta 4f XPS spectrum of both series of samples, a low energy shift of the absorption band characteristic of tantalum ions with an effective charge of (+5-δ) was observed. The XPS spectra of Bi4f7/2 and Bi4f5/2 also show a shift of bands towards lower energies which is attributed to the presence of some low-charge ions of transition elements in the bismuth position. The NEXAFS spectroscopy data showed that manganese ions in both series of samples have predominantly 2+ and 3+ oxidation states. XPS data indicate that in zinc-containing preparations the proportion of oxidized manganese ions is higher than in magnesium-containing ones.

The Pechini method was used for the first time to synthesize the phase-pure nickel-containing cubic pyrochlore Bi2NiNb2O9 (space group Fd-3m, a = 10.5371(5) angstrom), while the solid-phase reaction method provided no possibility to obtain impurities-free pyrochlore. At a synthesis temperature of 950 degrees C, low-porosity ceramics with indistinct grain boundaries were formed. The results of elemental mapping indicated a uniform distribution of metal atoms on the surface of the sample. The X-ray energy dispersive analysis showed that the chemical composition of the synthesized sample corresponded to the predetermined theoretical composition. The calcination of the sample synthesized by the Pechini method was studied by the thermal analysis up to 1100 degrees C. The functional composition of intermediate synthesis products was analyzed by vibrational spectroscopy (FTIR). In the FTIR spectrum of pyrochlore (4000-400 cm-1), absorption bands were identified at 829, 540, 654, and 490 cm-1. The dielectric properties of the pyrochlore were studied using an impedance spectroscopy. Pyrochlore Bi2NiNb2O9 has the high relative dielectric permittivity of 145 and low dielectric losses of 0.001 (at 24 degrees C, 1 MHz), which make it a promising for dielectric in multilayer ceramic capacitors.

Excellent dielectric properties, possibility of regulation of dielectric properties by electric field, low sintering temperature and chemical compatibility with fusible copper conductors make oxide bismuth-containing pyrochlores promising as dielectrics for multilayer ceramic capacitors, tunable microwave dielectric components, and devices for microwave applications. In this work, the concentration stability region of Mg-doped bismuth tantalate pyrochlore was experimentally determined. Based on the study, the conditions for the formation of mixed pyrochlores doped with divalent ions exhibiting a preference for octahedral positions are given. The concentration stability region of magnesium-containing pyrochlores based on bismuth tantalate (Bi2+xMg1+yTa2-yO9-delta , -0.11 <= x <= 0.325, -0.01 <= y <= 0.20) was experimentally determined. On the basis of experimental data, the conditions for the formation of mixed pyrochlores containing ions of divalent elements (Mg(II) type) in Ta(V) octahedral positions were defined. It was shown that phase-pure pyrochlores are formed in the case of a bismuth sublattice vacant, by 37 - 22.5 at.%, and the degree of substitution of cations of the Ta(V) octahedral sublattice by magnesium ions is limited to the interval 33 - 40 %. As SEM studies have shown, an increase in the bismuth content and the Mg / Ta molar ratio in the samples leads to the enlargement of grains and a decrease the pores of the ceramics.

The modified sol-gel method (Pechini method) is shown to synthesize multielement oxides on the basis of bismuth niobate that crystallize in the pyrochlore structure (space group Fd-3m). The temperature for the synthesis of a single-phase sample amounts to 950°C, which is 100°C lower than the calcination temperature used in the conventional ceramic method of synthesis. The average crystallite size determined radiographically varies from 39 nm (850°C) to 48 nm (1050°C) depending on the sintering temperature. According to x-ray diffraction analysis, the unit cell parameter is equal to 10.4872(6) Å. The conducted elemental mapping indicates a uniform distribution of metal atoms on the sample surface, while energy dispersive x-ray analysis shows that the chemical composition of the synthesized sample corresponds to the specified theoretical composition.

The concentration stability region of magnesium- containing pyrochlores based on bismuth tantalate (Bi2+xMg1+yTa2-yO9-delta, -0.11 <= x <= 0.325, -0.01 <= y <= 0.20) was experimentally determined. On the basis of experimental data the conditions for the formation of mixed pyrochlores containing ions of divalent elements (Mg(II) type) in Ta(V) octahedral positions were defined. It was shown that phasepure pyrochlores are formed in the case of a vacant, by 37-22.5 at.%, bismuth sublattice, and the degree of substitution by magnesium ions of cations of the Ta(V) octahedral sublattice is limited to the interval 33-40 %. It was demonstrated that magnesium(II) ions within 4-6 at.% are distributed in the bismuth position. It was found that the degree of substitution of the octahedral sublattice ions is not affected by the degree of the bismuth sublattice vacancy. It was shown that the condition of observing the permissible substitution of Ta(V) ions is equal to the requirement of achieving the average charge of B cations of the B2O6 octahedral sublattice to the value +4. Apparently, this is the second factor of pyrochlore structure preservation, equal to the tolerance factor, suitable for predicting the homogeneity region of mixed pyrochlores.

Bismuth-containing chromates, BixCrO1.5x+3 , were synthesized using a ceramic method from bismuth (III) and chromium (III) oxides, with a variable molar ratio of 1 ≤ n (Bi)/n (Cr) ≤ 38. The calcined samples exhibit a color variation from green to dark red, depending on the n (Bi)/n (Cr) ratio. The ceramic materials undergo a color change from green to red when a mixture of oxides with a significant predominance of bismuth oxide n (Bi2O3)/n (Cr2O3) ≥ 3 is subjected to a high-temperature treatment in air (at 650°C). It is noteworthy that the calcination of chromium (III) oxide under similar conditions occurs without the oxidation of chromium ions. X-ray diffraction analysis confirmed the formation of chromates, including Bi6Cr2O15, Bi10Cr2O21, Bi31Cr5O61.5, and Bi14CrO24 . X-ray spectroscopy studies of the samples revealed that the NEXAFS Cr2p spectra of the red bismuth-chromium ceramics exhibited similarities in the main details of the K2CrO4 spectrum, indicating the presence of chromium in the oxide ceramics in the form of tetrahedral CrO_4^2- ions. In addition, scanning electron microscopy data demonstrated that the samples exhibited a dense, low-porosity microstructure.

The study investigated the formation of inhomophase ceramics through Zn doping in Bi 2 & Scy; rTa 2 O 9.5-Delta . It was found that all Bi 2 Zn x Cr 1- x Ta 2 O 9.5-Delta (0.3 <= x <= 0.7) investigated samples crystallized in the pyrochlore structural type (sp. Gr. Fd-3m ) and contained an admixture of triclinic beta- BiTaO 4 (up to 24 wt %, sp. gr. P-1 ), with the admixture concentration proportional to the degree of zinc doping. It was shown that impurities in the samples could be eliminated by creating a defective bismuth sublattice proportional to the impurity content, resulting in single-phase Bi 2- y Zn x Cr 1- x Ta 2 O 9.5-Delta ( y <= 0.5, 0.3 <= x <= 0.7) samples with the pyrochlore structure. The unit cell parameter of pyrochlore increased with an increase in zinc ion content in the samples from 10.4493 & Aring; ( x = 0.3) to 10.4976 & Aring; ( x = 0.7). The microstructure of ceramics was represented by individual slightly melted grains 0.5-2 mu m in size, which increased in size and fuse with each other with an increase in zinc content. The near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) data showed that zinc doping did not change the oxidation degree of bismuth and tantalum in pyrochlore, with the ions in charge states Bi( +3), Zn( +2) and Ta( +5). The study also observed an energy shift of the absorption band in the Ta 4f spectrum toward lower energies ( Delta E = 0.55 eV) characteristic of tantalum ions with an effective charge ( +5- delta ) and a shift of the Bi 4f 7/2 and Bi 4f 5/2 bands shift to lower energies with increase in x (Zn), due to the distribution of some Zn (II) ions in the bismuth position. The oxidation degree of chromium ions in the samples was mainly ( +3), with some chromium ions oxidized and having an oxidation degree close to ( +6) according to NEXAFS data. The studied ceramics showed promise as dielectrics for multilayer ceramic capacitors and devices for microwave applications due to their low sintering temperature and high porosity.

New remains of a Taymyr mammoth, including bones, bone collagen, hairs, skin, and soft (muscle and fat) tissues were studied comprehensively by mineralogical, spectroscopic, chromatographic, and isotope-geochemical methods. The results were used to infer the mammoth’s biological age and diet, paleoclimatic conditions, and the mechanisms and degree of fossilization of the remains.

A cubic pyrochlore with the composition Bi1.865Co1/2Fe1/2Ta2O9+Δ (space group Fd-3m, a = 10.5013(8) Å) was synthesized from oxide precursors using solid-phase reactions. These ceramics are characterized by a porous microstructure formed by randomly oriented grains of an elongated shape with a longitudinal size of 0.5–1 µm. The electronic state of cobalt and iron ions in oxide ceramics was studied by NEXAFS and XPS spectroscopy. The parameters of the XPS spectra of Bi4f, Bi5d, Ta4f, Co2p, and Fe2p ionization thresholds for a complex pyrochlore were compared with the parameters of the corresponding oxides of the transition elements. The energy position of the XPS-Ta4f and -Ta5p spectra is shifted towards lower energies compared to the binding energy in tantalum(V) oxide by 0.75 eV. According to XPS spectroscopy, bismuth and tantalum cations have the corresponding effective charge of +3 and +(5-δ). The NEXAFS-Fe2p spectrum of ceramics coincides with the spectrum of Fe2O3 in its main spectrum characteristics and indicates the content of iron ions in the oxide ceramics in the form of octahedral Fe(III) ions, and according to the character of the Co2p spectrum, cobalt ions are predominantly in the Co(II) state.

A novel 312-type MAX-phase solid solution series in the Zr-Ti-Si-C system has been synthesized by the vacuum carbosilicothermic reduction method using mixtures of TiO2, ZrO2, SiC, and Si powders as starting materials. The upper limit for Zr content in metal sublattice of the synthesized (Zr,Ti)3SiC2 MAX phase solid solutions was found to be as much as approximately 66 at%, closely corresponding to a hypothetical quaternary Zr2TiSiC2 MAX phase. A wide miscibility gap inside the interval of Zr content in metal sublattice ranging between 22 at% and 55 at% was found. Crystal structure of the synthesized MAX-phase solid solutions was studied by HR-STEM/HAADF and XRD Rietveld analyses. The lattice constants were determined to be linearly correlated with Zr content as predicted by Vegard's law. A significant inhomogeneity in distribution of metal atoms similar to that of out-of -plane ordered quaternary MAX phases has been established for both Ti-rich and Zr-rich MAX-phase solid solutions.