Preparation of β-Ca<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>/Poly(D,L-lactide) and β-Ca<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>/Poly(ε-caprolactone) Biocomposite Implants for Bone Substitution

Highly permeable macroporous implants of various architectures for bone grafting have been fabricated by thermal extrusion 3D printing using highly filled β-Ca₃(PO₄)₂/poly(D,L-lactide) (degree of filling up to 70 wt %) and β-Ca₃(PO₄)₂/poly(ε-caprolactone) (degree of filling up to 70 wt %) composite filaments. To modify the surface of the composite macroporous implants with the aim of improving their wettability by saline solutions, we have proposed exposing them to a cathode discharge plasma (2.5 W, air as plasma gas) in combination with subsequent etching in a 0.5 M citric acid solution. It has been shown that the main contribution to changes in the wettability (contact angle) of the composites is made by the changes produced in their surface morphology by etching in a low-temperature plasma and citric acid. An alternative approach to surface modification of the composites is to produce a carbonate hydroxyapatite layer via precipitation from a simulated body fluid solution a factor of 5 supersaturated relative to its natural analog (5xSBF).     

Crystal structure of a Np(V) sesquioxalate,Na<Subscript>4</Subscript>(NpO<Subscript>2</Subscript>)<Subscript>2</Subscript>(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>3</Subscript>·2H<Subscript>2</Subscript>O

The crystal structure of a previously unknown Np(V) sesquioxalate, Na₄(NpO₂)₂(C₂O₄)₃·2H₂O was studied. The crystal structure consists of neptunyl(V) cations, sodium cations, oxalate anions, and water molecules of crystallization. Neptunyl(V) cations and oxalate ions form anionic chains [(NpO₂)₂(C₂O₄)₃] _n ^4n? . The coordination polyhedron (CP) of Np (pentagonal bipyramid) contains two apical “yl” oxygen atoms and five equatorial O atoms of three oxalate ions. The CP of Na(1) and Na(2) cations are combined through the common edges into zigzag chains in the [010] direction. Two independent oxalate ions are tridentate and tetradentate ligands.     

Mechanism of UO<Subscript>2</Subscript>(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>·6H<Subscript>2</Subscript>O decomposition under the action of microwave radiation

The effect of microwave radiation (MWR) on the decomposition of UO₂(NO₃)₂·6H₂O was studied. Determination of [UO ₂ ²⁺ ] and [NO ₃ ^? ], and also of the molar ratio NO ₃ ^? : UO ₂ ²⁺ in various fractions of the decomposition product showed that the mechanism of the UO₂(NO₃)₂·6H₂O decomposition under the action of MWR differs from the mechanism of its decomposition under common convection heating. The main precursor of UO₃ as product of UO₂(NO₃)₂·6H₂O decomposition under the action of MWR is uranyl hydroxonitrate UO₂(OH)NO₃ formed already in the first minutes of the irradiation. In contrast to the thermolysis under convection heating, UO₂(NO₃)₂ or its hydrates were not detected as intermediates. The mechanism of the UO₂(NO₃)₂·6H₂O decomposition under the action of MWR can be presented by the reactions UO₂(NO₃)₂·6H₂O → UO₂(OH)NO₃ + 5H₂O + HNO₃ and UO₂(OH)NO₃ → UO₃ + HNO₃. The solubility of UO₂(OH)NO₃ in H₂O at 20°C was estimated experimentally at 6.83 × 10^?2 M.     

Microwave dielectric properties of temperature-stable (Mg<Subscript>0.95</Subscript>Co<Subscript>0.05</Subscript>)<Subscript>2</Subscript>TiO<Subscript>4</Subscript>–Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite ceramics for LTCC applications

In this paper, the effects of Li₂O–B₂O₃–Bi₂O₃–SiO₂ (LBBS) glass on the phase formation, sintering characteristic, the microstructure and microwave dielectric properties of temperature-stable (Mg_0.95Co_0.05)₂TiO₄–Li₂TiO₃ ceramics were investigated. (Mg_0.95Co_0.05)₂TiO₄–Li₂TiO₃ powders were obtained by using the traditional solid-state process. A small amount of LBBS doping can effectively reduce sintering temperature and promote the densification of the ceramics. X-ray diffraction analysis revealed not only the primary phase (Mg·Co)₂TiO₄ associated with Li₂TiO₃ minor phase but also a third phase (Mg·Co)TiO₃. The dielectric constant and Qf values vary with the doping amount of LBBS and sintering temperatures. With the compensation of the positive temperature coefficient (τ _f ) of Li₂TiO₃ and the negative τ _f of (Mg_0.95Co_0.05)₂TiO₄, the τ _f of the specimens fluctuates around zero. The (Mg_0.95Co_0.05)₂TiO₄ ceramic with 2.5 wt% LBBS addition and sintering at 900?°C for 4 h exhibited excellent microwave dielectric properties: ? _r ?=?19.076, Qf?=?126100 GHz, and τ _f ?=?0.98 ppm/°C.     

Mechanism of UO<Subscript>2</Subscript>(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>·6H<Subscript>2</Subscript>O decomposition under the action of microwave radiation: Part 2

Products of UO₂(NO₃)₂·6H₂O decomposition under the action of microwave radiation (MWR) were studied by thermal gravimetric analysis, X-ray phase analysis, IR spectroscopy, and electron microscopy. The results of physicochemical studies of these decomposition products were compared to the published data for various uranium compounds, including UO₂(NO₃)₂·6H₂O. Apart from gaseous products, the final products of decomposition of 2–10 g of UO₂(NO₃)₂·6H₂O under the action of MWR for 35 min (the maximal process temperature, 170–320°C, is attained in the first 2–5 min of irradiation) are uranyl hydroxonitrate UO₂(OH)NO₃ and uranium trioxide UO₃ or their hydrates. The results obtained are consistent with the mechanism suggested in our previous paper and involving the reactions (1) UO₂(NO₃)₂·6H₂O → UO₂(OH)NO₃ + 5H₂O + HNO₃ and (2) UO₂(OH)NO₃ → UO₃ + HNO_3. The physicochemical study confirms the conclusions on the composition of products of UO₂(NO₃)₂·6H₂O decomposition under the action of MWR, made previously on the basis of chemical studies. The only precursor of UO₃ in microwave treatment of UO₂(NO₃)₂·6H₂O is UO₂(OH)NO₃ (or its hydrates). This is the main difference between the courses of uranyl nitrate decomposition under the conditions of microwave and convection heating. In the latter case, uranyl nitrate and its hydrates also participate in the formation of UO₃.     

Theoretical Studies of Electronic Paramagnetic Resonance <Emphasis Type="Italic">g</Emphasis> Factors for La<Subscript>2</Subscript>Mg<Subscript>3</Subscript>(NO<Subscript>3</Subscript>)<Subscript>12</Subscript>⋅24H<Subscript>2</Subscript>O

Lanthanum magnesium double nitrate (LMN) crystals can be used as material for adiabatic demagnetization, magnetic thermometers and a proton spin-polarized target in both physics and polarized neutron diffraction. In the past years, the double nitrates doped with transition metal or rare earth ions have been studied by experimental and theoretical methods. For instance, the electronic paramagnetic resonance (EPR) g factors of the Ce³⁺ ions in La₂Mg₃(NO₃)₁₂⋅24H₂O crystal were measured decades ago. But until now, these useful experimental results have not been theoretically explained. In this work, The EPR g factors of the trigonal Ce³⁺ centers in La₂Mg₃(NO₃)₁₂⋅24H₂O are theoretically studied from the perturbation formulae of the EPR parameters for a 4f¹ ion under the trigonal symmetry crystal field. The used crystal parameters are obtained from the superposition model and the local structure of the studied crystal. The calculated results are reasonably constant to the observed values. The results are discussed.     

Phase relations in the K<Subscript>2</Subscript>MoO<Subscript>4</Subscript>–Ln<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>–Zr(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> (Ln = La–Lu,Y) systems

We have studied phase relations in the K₂MoO₄–Ln₂(MoO₄)₃–Zr(MoO₄)₂ (Ln = La–Lu, Y) systems by the method of “intersecting cuts,” identified pseudobinary joins in their composition triangles, and constructed their phase compatibility diagrams. The systems have been shown to contain new ternary molybdates with the general formula K₅LnZr(MoO₄)₆ (Ln = Dy–Lu and Y). The thermal characteristics of the synthesized compounds have been studied by differential scanning calorimetry in the temperature range 25–700°C. The new ternary molybdates crystallize in a trigonal structure (sp. gr. R\(\bar 3\)c, Z = 6).     

Microwave dielectric properties of Sr<Subscript>0.7</Subscript>Ce<Subscript>0.2</Subscript>TiO<Subscript>3</Subscript>–Sr(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> ceramics

xSr_0.7Ce_0.2TiO₃–(1???x)Sr(Mg_1/3Nb_2/3)O₃ ceramics, referred to xSCT–(1???x)SMN, were successfully produced by conventional solid-state sintered technology. The compounds, belonging to perovskites with a secondary phase of CeO₂, can be detected even with x down to 0.1 of SCT composition. The overall trend for grain growth illustrates the increase with increasing SCT doping level. The Raman peak at 825 cm^?1 splits into two peaks and causes red shift phenomenon. XPS spectra indicate that Ti and Nb ions exist respectively in tetravalence and pentavalence, and Ce ions exist in trivalence and tetravalence. Dielectrics constant (ε _r ) of SCT–SMN ceramics gradually increases with increasing theoretical dielectric polarizabilities. A wider width of the 825 cm^?1 for FWHM of A_1g mode Raman peaks suggests to a lower Q?×?f value. The increasing tolerance factor in agreement with temperature coefficient of resonant frequency (τ _f ), denotes that the rise of perovskite symmetry. The 0.1SCT–0.9SMN ceramic sintered at 1450?°C for 4 h illustrates excellent microwave dielectric properties with ε _r ?~?35.4, Q?×?f?~?11282 GHz and τ _f ?~?1.7 ppm/°C. Activation energies of 0.1SCT–0.9SMN ceramic at 100, 300 and 500 V, are ~0.436, 0.427 and 0.331 eV, respectively, indicative of a decreased trend with external electric field.     

Ferroelectric and antiferroelectric polarisation switching characteristics of Bi(Mg<Subscript>0.5</Subscript>Ti<Subscript>0.5</Subscript>)O<Subscript>3</Subscript>–PbTiO<Subscript>3</Subscript> ceramics

Bi(Mg_0.5Ti_0.5)O₃–PbTiO₃ (BMT–PT) ceramics, with BMT–PT ratios ranging from 70-30 to 50-50, were prepared by a conventional solid state reaction process. The 50-50 BMT–PT ceramic possessed a tetragonal perovskite structure with a c/a ratio of ~1.037. Increasing BMT content led to a reduction of tetragonality and a change of structure to a rhombohedral or pseudo-cubic phase. Dielectric measurements, carried out during heating, indicated the occurrence of two phase transformations, which were identified as relaxor ferroelectric to antiferroelectric (at a temperature in the range from 150–300 °C) and antiferroelectric to paraelectric (at a temperature around 500 °C). The antiferroelectric nature of the 60-40 and 70-30 BMT–PT ceramics in the intermediate temperature range was confirmed by polarisation-electric field hysteresis measurements.     

Crystal Structure of Uranyl Malonate Trihydrate [UO<Subscript>2</Subscript>(OOC)<Subscript>2</Subscript>CH<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)]·2H<Subscript>2</Subscript>O

Single crystals of [UO₂(OOC)₂CH₂(H₂O)]·2H₂O (I) were prepared by recrystallization of finely crystalline uranyl malonate trihydrate under hydrothermal conditions. The crystal structure of I consists of electroneutral [UO₂(OOC)₂CH₂(H₂O)]_n layers and water molecules located between them. The uranium coordination number is 7. The uranium coordination polyhedron is a distorted pentagonal bipyramid with the oxygen atoms of the uranyl group in the apices. The equatorial plane is occupied by four O atoms of three malonate ligands and the water molecule. The malonate anion is coordinated in the bidentate fashion to one uranyl ion to form a six-membered ring and in the monodentate fashion to two other uranyl ions.     

Sol–gel preparation and high-energy XRD study of (CaO)<Subscript>x</Subscript>(TiO<Subscript>2</Subscript>)<Subscript>0.5−x</Subscript>(P<Subscript>2</Subscript>O<Subscript>5</Subscript>)<Subscript>0.5</Subscript> glasses (x = 0 and 0.25)

Glasses from the CaO–TiO₂–P₂O₅ system have potential use in biomedical applications. Here a method for the sol–gel synthesis of the ternary glass (CaO)_0.25(TiO₂)_0.25(P₂O₅)_0.5 has been developed. The structures of the dried gel and heat-treated glass were studied using high-energy X-ray diffraction. The structure of the binary (TiO₂)_0.5(P₂O₅)_0.5 sol–gel was studied for comparison. The results reveal that the heat-treated (CaO)_0.25(TiO₂)_0.25(P₂O₅)_0.5 glass has a structure based on chains and rings of PO₄ tetrahedra, held together by a combination of electrostatic interaction with Ca²⁺ ions and by corner-sharing oxygen atoms with TiO₆ octahedra. In contrast, the (TiO₂)_0.5(P₂O₅)_0.5 glass has a structure based on isolated P₂O₇ units linked together by corner-sharing with TiO₆ groups. The results suggest that both the dried gels possess open porous structures. For the (CaO)_0.25(TiO₂)_0.25(P₂O₅)_0.5 sample there is a significant increase in Ca–O coordination number with heat treatment.     

Phase formation and dielectric properties of ceramics in the BiFeO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript>–Bi(Mg<Subscript>0.5</Subscript>Ti<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> system

We have studied the effect of Bi(Mg_0.5Ti_0.5)O₃ additions on the phase formation, structural parameters, microstructure, and dielectric properties of solid solutions in the region of a morphotropic phase boundary in the BiFeO₃–BaTiO₃ system. Single-phase samples with the perovskite structure have been obtained and the addition of Bi(Mg_0.5Ti_0.5)O₃ has been shown to raise the Curie temperature of the ceramics and improve their dielectric properties.     

Thermodynamic properties of (TeO<Subscript>2</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>(MoO<Subscript>3</Subscript>)<Subscript>1–<Emphasis Type="Italic">n</Emphasis></Subscript> glasses

The thermal behavior of (TeO₂) _n (MoO₃)_1–n (n = 0.75, 0.85, 0.90) tellurite glasses has been studied by differential scanning calorimetry in the range from T = 300 to T = 850 K and heat capacity has been measured in the temperature range. The thermodynamic characteristics of the devitrification process and glassy state have been determined. The experimental data obtained have been used to evaluate the standard thermodynamic functions of the system in glassy and supercooled liquid states: heat capacity C _p °(T), enthalpy H°(T)–H°(320), entropy S°(T)–S°(320), and Gibbs function G°(T)–G°(320) in the temperature range 320–630 K. The composition dependences of the glass transition temperature and thermodynamic functions for the glasses have been obtained. The thermal and thermodynamic properties of the tellurite glasses have been compared to those of previously studied (TeO₂) _n (WO₃)_1–n and (TeO₂) _n (ZnO)_1–n glasses.     

Crystal Structure of a Double Neptunium(V) Lanthanum Nitrate,La(NpO<Subscript>2</Subscript>)<Subscript>3</Subscript>(NO<Subscript>3</Subscript>)<Subscript>6</Subscript>·<Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O

The structure of a double neptunium(V) lanthanum nitrate, La(NpO₂)₃(NO₃)₆·nH₂O, was studied by single crystal X-ray diffraction. Each neptunyl(V) ion in the structure of the compound is bonded to four other neptunyl(V) ions, acting simultaneously as a bidentate ligand and as a coordination center for two other dioxocations. The cation-cation interaction of the neptunyl(V) ions results in formation of trigonal-hexagonal cationic networks. The surrounding of each Np atom also includes two bidentate nitrate ions. The CN of the Np atom is 8, and the coordination polyhedron is a distorted hexagonal bipyramid. The La³⁺ cations are surrounded only by water molecules.     

Good thermal stability and improved piezoelectric properties of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript>–Bi(Mg<Subscript>0.75</Subscript>W<Subscript>0.25</Subscript>)O<Subscript>3</Subscript> solid solutions

In this paper, (1 ? x)(K_0.5Na_0.5)NbO₃–xBi(Mg_0.75W_0.25)O₃ (x = 0–0.015) lead-free dielectric ceramics were investigated. XRD analysis certified that the Bi(Mg_0.75W_0.25)O₃ has diffused into (K_0.5Na_0.5)NbO₃ to fabricate a new solid solution. The addition of Bi(Mg_0.75W_0.25)O₃ depressed the orthorhombic–tetragonal phase transition temperature from 210 to 176 °C and tetragonal–pseudocubic phase transition temperature (Curie point) from 419 to 400 °C. As x = 0.005, the ceramics exhibited high relative permittivity (ε ~ 1325), low dielectric loss (tan δ < 2.9%) tan δ stability (Δε/ε_168°C ≤ ±15%) in the temperature range of 168 ~ 369 °C. Especially, the ceramics also showed optimized piezoelectric constant (d ₃₃ = 122 pC N^?1) and remnant polarization (P_r = 32.57 μC cm^–2). These results indicated that the BMW added ceramics have potential applications in ferroelectric and thermal stability devices.     

Effect of gamma radiation on electrical and optical properties of (TeO<Subscript>2</Subscript>)<Subscript>0·9</Subscript> (In<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>0·1</Subscript> thin films

We have studied in detail the gamma radiation induced changes in the electrical properties of the (TeO₂)_0·9 (In₂O₃)_0·1 thin films of different thicknesses, prepared by thermal evaporation in vacuum. The current–voltage characteristics for the as-deposited and exposed thin films were analysed to obtain current versus dose plots at different applied voltages. These plots clearly show that the current increases quite linearly with the radiation dose over a wide range and that the range of doses is higher for the thicker films. Beyond certain dose (a quantity dependent on the film thickness), however, the current has been observed to decrease. In order to understand the dose dependence of the current, we analysed the optical absorption spectra for the as-deposited and exposed thin films to obtain the dose dependences of the optical bandgap and energy width of band tails of the localized states. The increase of the current with the gamma radiation dose may be attributed partly to the healing effect and partly to the lowering of the optical bandgap. Attempts are on to understand the decrease in the current at higher doses. Employing dose dependence of the current, some real-time gamma radiation dosimeters have been prepared, which have been found to possess sensitivity in the range 5–55 μGy/μA/cm². These values are far superior to any presently available real-time gamma radiation dosimeter.     

Effect of excess Pb on microstructures and electrical properties of 0.67Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>–0.33PbTiO<Subscript>3</Subscript> ceramics

0.67Pb(Mg_1/3Nb_2/3)O₃–0.33PbTiO₃ (PMNT) ceramics were fabricated by using their powders synthesized through a sol–gel process. Excess Pb(CH₃COO)₂·3H₂O (0, 2, 5, 10 or 15 mol%) was added to the starting materials to study the effect of excess Pb on the microstructures, ferroelectric and dielectric properties of the PMNT ceramics. All the X-ray diffraction peaks can be indexed using perovskite-type PMNT for the ceramics prepared with excess Pb, while the PMNT ceramics with no excess Pb contain a little pyrochlore phase. The PMNT ceramics prepared with 2 mol% excess Pb are dense and uniform and composed of grains ranging from 3 to 7 μm. They exhibit the largest remnant polarization (P _r = 32.1 μC/cm²) and the highest peak dielectric constant (ε _max = 12,725). When more than 2 mol% excess Pb added, the electrical properties of the PMNT ceramics decreased with increasing excess Pb. Too much excess Pb (over 10 mol%) resulted in abnormal grain growth (>20 μm), large pores and residual PbO in amorphous state in PMNT ceramics, and they impaired the ferroelectric and dielectric properties of PMNT ceramics greatly.     

Microwave and photoluminesent characterizations of (Ca<Subscript>2</Subscript>Mg<Subscript>3</Subscript>)(X<Subscript>1.75</Subscript>Sb<Subscript>0.25</Subscript>)TiO<Subscript>12</Subscript> [X = Nb and Ta] ceramics

(Ca₂Mg₃)(X_1.75Sb_0.25)TiO₁₂ [X = Nb and Ta] ceramics are prepared through the conventional solid-state route. The samples are calcined at 1,100 and 1,180 °C, and are sintered at 1,250 and 1,375 °C. The substitution of Sb decreases the calcination and sintering temperatures of pure (Ca₂Mg₃)(Nb/Ta)₂TiO₁₂. The structure of the samples is analyzed using X-ray diffraction method. The microstructure of the sintered pellet is studied using scanning electron microscopy. The dielectric properties such as dielectric constant (ε_r), quality factor (Q_uxf) and temperature coefficient of resonant frequency (τ_f) are measured in the microwave frequency region. By Sb substitution, thermal stability is achieved, with the increase in dielectric constant, without much change in the quality factor. The materials have intense emission lines in the wavelength region 500–700 nm. The compositions have good microwave dielectric properties and photoluminescence and hence are suitable for dielectric resonator and ceramic laser applications.     

Investigation on the synthesis of (Zn<Subscript>1−x</Subscript>Mg<Subscript>x</Subscript>)TiO<Subscript>3</Subscript> and the modulation effect of CaTiO<Subscript>3</Subscript>

(Zn_1−xMg_x)TiO₃ (x = 0.1–0.5) solid solutions were synthesized by solid-state reaction using ZnO, (MgCO₃)₄·Mg(OH)₂·5H₂O and TiO₂ as raw materials. The influences of Zn: Mg ratio and calcining temperature on the properties of (Zn_1−xMg_x)TiO₃ were studied. By adding CaTiO₃ into (Zn_1−xMg_x)TiO₃, the microwave properties and sintering behavior were improved. The ceramics could be sintered at 1150 °C, and the ceramics with excellent microwave properties of τ_f ≈ ±10 ppm/°C, ε ≈ 24, Q × f > 45000 GHz (8 GHz) were obtained.     

Synthesis and Structure of the Np(VII) Complex with Guanidinium,Li[C(NH<Subscript>2</Subscript>)<Subscript>3</Subscript>]<Subscript>2</Subscript>[NpO<Subscript>4</Subscript>(OH)<Subscript>2</Subscript>]·6H<Subscript>2</Subscript>O

The previously unknown Np(VII) compound Li[C(NH₂)₃]₂[NpO₄(OH)₂]·6H₂O (I), containing organic cations, was synthesized and studied by single crystal X-ray diffraction. In contrast to the relatively numerous structurally characterized salts of [NpO₄(OH)₂]^3– anions with Na⁺, K⁺, Rb⁺, and Cs⁺ cations, which were prepared only from strongly alkaline media, crystals of I were isolated from solutions with a very low concentration of OH^– ions (about 0.1 M). The compound is relatively stable in storage in the dry form, but is strongly hygroscopic. In the structure of I, there are two independent Np(VII) atoms with the oxygen surrounding in the form of tetragonal bipyramids. In contrast to the other salts of the [NpO₄(OH)₂]^3– anions with singlecharged alkali metal cations, the C(NH₂) ₃ ⁺ ions and hydrated Li⁺ ions in I interact with the oxygen surrounding of Np(VII) only via hydrogen bonds of types O_w–H···O and N–H···O with the formation of a three-dimensional H-bond network.