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1.
While samarium phosphate (Sm2O3) x (P2O5)(1?x) glasses are known to show pronounced long-wavelength acoustic-mode softening, their lanthanum (La2O3) x (P2O5)(1?x) analogues do not. To investigate experimentally this different influence of lanthanide modifiers, a comparative study has been made of the effects of temperature and pressure on the velocities of ultrasonic waves propagated in binary ((La2O3) x (P2O5)(1?x) and (Sm2O3) x (P2O5)(1?x)) and ternary ((La2O3) x (Sm2O3) y (P2O5)(1?x?y)) phosphate glasses with compositions near to that corresponding to the metaphosphate (R2O3)0.25(P2O5)0.75. For each glass the second-order elastic stiffness tensor componentsC IJ S continue to increase down to 10 K in a manner consistent with ultrasonic interactions with two-level systems. Measurements of the effects of hydrostatic pressure on the ultrasonic wave velocities have been used to determine the hydrostatic pressure derivatives (?C IJ S /?P) T,P=0 of the second-order elastic stiffness tensor components and (?B 0 S /?P) T,P=0 of the bulk modulusB 0 S at room temperature (293 K). For the ternary glasses (?C 11 S /?P) T,P=0, (?C 44 S /?P) T,P=0 and (?B 0 S /?P) T,P=0 are small but positive; these glasses stiffen under pressure. Replacement of samarium by lanthanum in the ternary glasses negates the acoustic-mode softening. Possible sources of the different effects of lanthanum and samarium modifiers on the non-linear acoustic properties of metaphosphate glasses are discussed.  相似文献   

2.
The speciation of Zr(IV) radionuclides at their concentration of ~10?13 M in the solution was studied. The pH ranges where Zr(IV) exists as ions or as pseudocolloids were determined. The Zr4+ hydrolysis yields Zr(OH)3+ and Zr(OH) 2 2+ complexes. Their stability constants were calculated. At [Zr(IV)] > 1 × 10?5 M, binuclear hydroxo complexes Zr2(OH) z+ x are formed.  相似文献   

3.
We describe a blue/green inorganic material, Ba3(P1???x Mn x O4)2 (I) based on tetrahedral MnO $_{4}^{3-}$ :3d 2chromophore. The solid solutions (I) which are sky-blue and turquoise-blue for x ≤ 0·25 and dark green for x ≥ 0·50, are readily synthesized in air from commonly available starting materials, stabilizing the MnO $_{4}^{3-}$ chromophore in an isostructural phosphate host. We suggest that the covalency/ionicity of P–O/Mn–O bonds in the solid solutions tunes the crystal field strength around Mn(V) such that a blue colour results for materials with small values of x. The material could serve as a nontoxic blue/green inorganic pigment.  相似文献   

4.
We have studied terbium substitution for ytterbium in (Yb0.9 ? x Tb x Ca0.1)2Ti2O7 ? ?? (x = 0.1, 0.2, 0.3, 0.4) pyrochlore solid solutions synthesized through coprecipitation followed by firing at 1550°C. The results indicate that only a small amount of terbium (less than 10%) can be incorporated into the pyrochlore structure of (Yb0.9Ca0.1)2Ti2O6.9 because of the large difference in ionic radius between the terbium and ytterbium cations: ??r = r(Tb CN 8 3+ ) ? r(Yb CN 8 3+ ) = 0.055 ?. The oxygen ion conductivity of the (Yb0.9 ? x Tb x Ca0.1)2Ti2O7 ? ?? solid solutions has been determined by impedance spectroscopy in air in the temperature range 300 to 900°C. At high temperatures (t > 640°C), their bulk conductivity was essentially independent of the Yb/Tb ratio. The observed decrease in density and microstructural changes were insignificant. At relatively low temperatures (t < 640°C), the bulk conductivity decreased slightly, and the decrease depended little on terbium concentration.  相似文献   

5.
The microwave dielectric properties of La(Mg0.5?xBaxSn0.5)O3 ceramics were examined with a view to their exploitation for wireless communications. The La(Mg0.5?xBaxSn0.5)O3 ceramics were prepared by the conventional solid-state method with various sintering temperatures. The La(Mg0.5?xBaxSn0.5)O3 ceramics contained La2Sn2O7. An apparent density of 6.54 g/cm3, a dielectric constant ( $ \varepsilon_{r} $ ε r ) of 20.1, a quality factor (Q  $ \times $ ×  f) of 51,600 GHz, and a temperature coefficient of resonant frequency ( $ \tau_{f} $ τ f ) of ?82 ppm/°C were obtained for La(Mg0.43Ba0.07Sn0.5)O3 ceramics that were sintered at 1,550 °C for 4 h.  相似文献   

6.
Single-phase sintered ceramic materials (ZrO2)1?x {(Y2O3) y (RE2O3)1-y x }x (RE=Nd, Ce, Dy, Er), were synthesized and electrical conductivity and transport number measurements were made as a function of temperature between 500 and 1200° C. The activation energies of conduction were determined, and it was found that the charge carriers in these solid solutions are oxygen ions. The fabricated electrolyte discs were used in cells of the type \(P_{O_2 }\) , Pt/zirconia solid solution/ \(P_{\mathop O\limits^{'} _2 }\) , platinum where \(P_{O_2 }\) =air (0.21 atm) and \(P_{\mathop O\limits^{'} _2 }\) =1 atm or argon-O2 mixtures. Below 700° C, the e.m.f. deviated from the theoretical values for completely ionic conduction; good agreement was observed above this temperature.  相似文献   

7.
Systematical studies of resistivity ??(T), thermopower S(T), and thermal conduction ??(T) have been performed on the electron-doped manganites La0.9Te0.1Mn1?x Cr(Al) x O3 (0.05??x??0.20). The Cr005 and Al005 samples exhibit an insulator-metal transition in the ??(T) curves, however, other samples present insulating behaviors in the whole measured temperature. The S(T) data increases with decreasing temperature and develop a peak at $T_{S}^{P}$ for all samples, with decreasing temperature further, another characteristic temperature $T_{s}^{m}$ is observed. The fits of ??(T) and S(T) data in the high temperature region are presented, and the result shows that the electron conduction is governed by the VRH mechanism for Al-doped samples and the SPC mechanism for Cr-doped ones. As to thermal conduction ??(T), it is suggested that it comes from two sides, one is the phonon-phonon scattering due to disorder and the other is the spin-phonon interaction.  相似文献   

8.
Bubbling of an ozone-oxygen mixture containing 0.1?C0.5 vol % O3 at a rate of 15?C20 l h?1 through 13 ml of a 2 × 10?5?1 × 10?4 M solution of Np(VI) in 0.1 and 1 M LiOH leads to the formation of Np(VII). The initial rate increases approximately in proportion to [Np(VI)] and [O 3 gas ]0.5. Up to 80% of Np(VI) is oxidized at maximum. At the O3 concentration in the gas phase increased to 1?C4 vol %, Np(VI) is oxidized completely. Under the same conditions, Np(VI) in a concentration of (1?C5) × 10?3 M is oxidized to almost 100%. Analysis of published data and additional experiments on the reaction of O3 with Np(VI) ions in LiOH solutions allow a conclusion that the ozonation involves the reactions O3 + OH? = HO 2 ? + O2, O3 + HO 2 ? + OH? = O 3 ? + O 2 ? + H2O, and O3 + O 2 ? = O 3 ? + O2, followed by O 3 ? + NpO2(OH) 4 2? = O2 + NpO4(OH) 2 3? + H2O. In addition, HO 2 ? reduces Np(VII) and Np(VI) and reacts with O 3 ? . Certain contribution is made by the reaction Np(VI) + O3 = Np(VII) + O 3 ? . The dependence of the Np(VII) accumulation rate on [O 3 gas ]0.5 was interpreted in terms of the concept of a heterogeneous-catalytic process.  相似文献   

9.
We have compared (Ln2 ? x Zr x )Zr2O7 + x/2 (Ln = Nd, Sm) pyrochlore-like solid solutions with interstitial oxide ion conduction and Ln2(Zr2 ? x Ln x )O7 ? δ (Ln = Nd, Sm) pyrochlore-like solid solutions with vacancy-mediated oxide ion conduction in the symmetric systems Nd2O3-ZrO2 (NdZrO) and Sm2O3-ZrO2 (SmZrO). We have studied their structure, microstructure, and transport properties and determined the excess oxygen content of the (Sm2 ? x Zr x )Zr2O7 + x/2 (x = 0.2) material using thermal analysis and mass spectrometry in a reducing atmosphere (H2/Ar-He). The Ln2 ± x Zr2 ± x O7 ± x/2 (Ln = Nd, Sm) solid solutions have almost identical maximum oxygen vacancy and interstitial conductivities: (3–4) × 10?3 S/cm at 750°C. The lower oxygen vacancy conductivity of the Ln2(Zr2 ? x Ln x )O7 ? δ (Ln = Nd, Sm; 0 < x ≤ 0.3) solid solutions is due to the sharp decrease in it as a result of defect association processes, whereas the interstitial oxide ion conductivity of the (Ln2 ? x Zr x )Zr2O7 + x/2 (Ln = Nd, Sm; 0.2 ≤ x < 0.48) pyrochlore-like solid solutions is essentially constant in a broad range of Ln2O3 concentrations.  相似文献   

10.
The pyrochlore $\mathrm{Er}_{2}^{3 +} \mathrm{Ti}_{2}^{4 +}\mathrm{O}_{7}^{2 -}$ was synthesized via a ceramic method using two different oxides (Er2O3 and TiO2). The compound was found to crystallize in the cubic system with the $\mathrm{Fd}\overline{3}\mathrm{m}$ space group (No. 227). A magnetic study, carried out at 2 and 300 K under an applied magnetic field ?? 0 H=0.05?T, has revealed a complex magnetic structure at low temperature. The effective paramagnetic moment $\mu_{\mathrm{eff}}^{\exp}$ , deduced from (????? 0)?1=f(T) curve, was found by assuming a zero moment on the transition metal atom Ti4+. The paramagnetic Curie?CWeiss temperature ?? CW=?21.54?K, the nearest neighbor interaction J nn =?2.30?K, the classical nearest neighbor J cl=?8.65?K and the dipolar D nn =3.76?K interactions?? values have revealed an antiferromagnetic behavior for Er2Ti2O7 compound at low temperature. We have also studied the effects of the magnetic field splitting of rare-earth atom Er3+ in the compound Er2Ti2O7 curved Arrott plots.  相似文献   

11.
Nano-sized B and Mg powders have been successfully deposited onto single crystal MgO(100) and Al2O3(001) substrates using 2.4 MHz ultrasonic spray pyrolysis system and an appropriate solution to obtain thin films of MgB2 superconductors. After an in-situ heating process, ??600?C1000 nm thick superconductor films were obtained. The microstructure, electrical, and magnetic properties were characterized by means of particle size analyzer, XRD, SEM?CEDX, R?CT, and M?CH analysis. The effect of particle concentration in the solution, spraying time, and heating temperature on the quality of the MgB2 films were discussed. The best T c and T zero results were obtained to be 39.5 and 37.4 K, respectively, for the film deposited on the Al2O3(001) substrates. Magnetic properties of the MgB2 films were investigated at 3 different temperatures and up to 5 T. Symmetric hysteresis loops for all temperature and field cases were obtained and maximum $J_{c}^{\mathrm{mag}}$ value was calculated to be 4.0×106 A?cm?2 at 10 K for 0 T for the film deposited on the Al2O3(001) substrates. The results obtained were found to be highly dependant on the particle concentration in the solution, heating temperature of substrates and carrier gas flow rate during spraying.  相似文献   

12.
Ca0.5Zr2(PO4)3:Eu2+, Sr0.5Zr2(PO4)3:Eu2+, and Ca0.5Zr2(PO4)3:Eu2+, Sm3+ orthophosphates prepared through precipitation using sol-gel processes are analogs of NaZr2(PO4)3 (NZP) and crystallize in space group R $\bar 3$ . Their crystallographic parameters determined by X-ray diffraction are consistent with the interatomic distances extracted from EXAFS data. Their luminescence spectra obtained under excitation in the range 300?C400 nm contain emission bands between 425 and 525 nm. Substitution of the larger sized cations Eu2+ and Sm3+ for Ca2+ shifts the emission bands to shorter wavelengths and reduces their width because of the decrease in the effect of the crystal field. Analysis of the spectra indicates that Eu2+ occupies two types of crystallographic sites (independent interstitial sites of different sizes and shapes in the NZP framework structure). Codoping with Eu and Sm has ensured luminescence with chromaticity coordinates approaching those of white light: (x = 0.27, y = 0.34).  相似文献   

13.
The anomalous magnetic properties of Pr ions in the PrBa2Cu3O6+x system are investigated at low temperature. Measurements of the specific heat C P(T) and the magnetic susceptibility χ(T) are performed on ceramic samples in the tetragonal structure with x=0.44 and x=0. Two new magnetic transitions are observed below the Néel temperature of the Pr antiferromagnetic ordering $T_{\mathrm{N}}^{\mathrm{Pr}} \sim 9\mbox{--}10~\mathrm{K}$ . The first one is observed at the low-critical temperature T cr~4–5?K and the second one is observed at $T_{2}^{\mathrm{Pr}\text{--}\mathrm{Cu}} \sim 6\mbox{--}7~\mathrm{K}$ , respectively. Assuming that ΔC P(T) can be used to represent the Pr contribution to the specific heat C P(T), the data are well fitted for T<T cr by using the development of ΔC P(T)/TA(T 2)?3/2 γ+M(T 2) 1 +m(T 2) 2 . The values of the electronic coefficient Δγ are found much lower than all previous results obtained in compounds of the orthorhombic structure, and this is, in good agreement with the insulating character of our non-superconducting samples. The high values obtained for the coefficient M, permits us to confirm the existence of strong Pr–Pr exchange interactions. Some non-linear effects attributed to the values of the coefficient m are revealed and discussed in terms of the previous Pr–Cu coupling with a spin reorientation phase transition of both spin sublattices around $T_{2}^{\mathrm{Pr}\text{--}\mathrm{Cu}}$ . The appearance of a weak ferromagnetic tendency in the magnetic susceptibility analysis below T cr, could be associated with the reordering of the Pr subsystem.  相似文献   

14.
The microwave dielectric properties of Zn2(Sn(1?x)Zrx)O4 ceramics were examined with a view to their exploitation for mobile communication. The Zn2(Sn(1?x)Zrx)O4 ceramics were prepared by the conventional solid-state method with various amount of Zr substitution. The diffraction peaks of Zn2(Sn(1?x)Zrx)O4 ceramics did not vary significantly as x varied. A density of 6.10 g/cm3 was obtained for Zn2(Sn0.99Zr0.01)O4 ceramic, sintered at 1,225 °C for 4 h. Dielectric constant (? r ) of 9.6, quality factor (Q × f) of 87,000 GHz, and temperature coefficient of resonant frequency (τ f ) of ?51 ppm/°C were obtained for Zn2(Sn0.99Zr0.01)O4 ceramics that were sintered at 1,225 °C for 4 h.  相似文献   

15.
A new oxalate complex, Na4(NpO2)2(C2O4)3·6H2O, with the Np:C2O4 ratio of 2:3 was synthesized and studied by single crystal X-ray diffraction. In the crystal, the NpO 2 + cations and oxalate anions are bound in open networks [(NpO2)2(C2O4)3] n 4n- parallel to the bc plane. The Na(1) cations are accommodated in large voids of the neptunyl oxalate networks with the formation of crimped mixed-cation layers of the composition [Na2(NpO2)2(C2O4)3] n 2n- . The negative charge of the layers is compensated by the Na(2) cations arranged between the layers. The Np atoms have a pentagonal bipyramidal coordination surrounding with the equatorial plane formed by the oxygen atoms of three oxalate anions. The structure contains tridentate-bridging and tetradentate-bridging oxalate anions.  相似文献   

16.
The (Tl0.5Pb0.5)Sr2(Ca1?x Te x )Cu2O7??? (Tl-1212) superconductor for x=0.0 to 0.5 has been prepared and studied by a powder X-ray diffraction method, electrical resistance and AC susceptibility measurements. Most of the samples showed Tl-1212 as the major phase and Tl-1201 as the minor phases. Small amounts of Te substitution (x??0.3) maintained the formation of the Tl-1212 phase but larger amounts led to the formation of 1201 and an unknown impurity phase. The resistance versus temperature curve showed metallic behavior for all samples. The resistance versus temperature curves showed onset transition temperature ( $T_{\mathrm{c\ onset}}$ ) between 92 and 97 K. Our results indicated the combined effects of Te substitution, heating temperature and heating time on the formation and optimization of the (Tl0.5Pb0.5)Sr2(Ca1?x Te x )Cu2O7 superconductor.  相似文献   

17.
The dynamic spin susceptibility $\chi^{+,-}_{\mathrm{total}}(\omega,{\bf q})$ that takes into account the interplay of localized and itinerant charge carriers exhibits a diffusive-like, extremely narrow and sharp symmetric ring of maxima at very small wave vectors: $|{\bf q}|=q_{0}$ where q 0ω/J≈10?6 with the Nuclear Magnetic Resonance (NMR) frequency ω and the superexchange coupling constant J together with the peak at the antiferromagnetic wave vector Q=(π,π). The calculated plane copper 63(1/T 1) and oxygen 17(1/T 1) nuclear spin-lattice relaxation rates from carrier-free right up to optimally doped La2?x Sr x CuO4 are in good agreement with experimental data.  相似文献   

18.
Synthesis and the results of IR and single crystal X-ray diffraction study of Na4(UO2)4(i-C4H9COO)11·(NO3)·3H2O are reported. The crystals are monoclinic; the unit cell parameters at 100 K are as follows: a = 13.697(2), b = 20.285(3), c = 15.991(3) Å, β = 103.760(3)°, space group P21, Z = 2, R = 0.0650. The uraniumcontaining structural units are mononuclear moieties [UO2(i-C4H9COO)3]? and [UO2(NO3)(i-C4H9COO)2]?, belonging to crystal-chemical group AB 3 01 (A = UO 2 2+ , B01 = i-C4H9COO? and NO 3 ? ) of uranyl complexes. The IR data are consistent with the results of the single crystal X-ray diffraction study. The influence of the carboxylate ligand volume on the structure of Na[UO2L3nH2O crystals (L = acetate, n-butyrate, isovalerate ion) is analyzed.  相似文献   

19.
Piezoceramic compositions Pb1?zLaz(NiSb)0.05[(Zr0.52Ti0.48)1?Z/4]0.95O3 with Z = 0.01–0.05 were synthesized by mixed oxide route to study the effect of Lanthanum (La) on crystal structure, microstructure, piezoelectric and ferroelectric properties. Calcination was performed at 1,060 °C and sintering at 1,270 °C for 1 h. X-Ray diffraction pattern indicated the polycrystalline microstructure along with co-existence of tetragonal and rhombohedral perovskite phases. Dielectric constant ( $ K_{3}^{T} $ ) was increased whereas piezoelectric voltage constant (g 33) was decreased with increase in lanthanum. Dense microstructure was observed for the composition containing 3 mol% of lanthanum. This was resulted in optimum piezoelectric charge constant (d 33 = 468 × 10?12 C/N), electromechanical coupling factor (k p  = 0.68), remanent polarization (P r = 24.65 μC/cm2) and displacement (D = 2,012 nm). Results indicated that the composition Pb0.97La0.03(NiSb)0.05[(Zr0.52Ti0.48)0.9925]0.95O3 could be suitable for actuator applications. The composition Pb0.98La0.02(NiSb)0.05[(Zr0.52Ti0.48)0.995]0.95O3 resulted into moderately high value of voltage constant (g 33 = 39.3 × 10?12 V m/N) and optimum value of Figure of Merit (d 33 × g 33 = 16.2 × 10?12 C V m/N2) indicated the usefulness for sensor and power harvesting applications.  相似文献   

20.
Ba1???x Bi x (Ti0·9Zr0·1)1???x Fe x O3 ( x = 0–0·075) ceramics are prepared using a conventional solid state reaction method. X-ray diffraction shows the presence of a single phase. Addition of Bi3?+? and Fe3?+? strongly influences the crystal structure and dielectric properties of the ceramics. The evolution from a normal ferroelectric to a relaxor ferroelectric is emphasized. Ba0·99Bi0·01(Ti0·9Zr0·1)0·99Fe0·01O3 ceramic shows a relaxor behaviour at room temperature with Δ T m =12 K. PE hysteresis loop of the composition, x = 0·007, shows a remanent polarization ( P r ) of 0·5 μC/cm2 with a coercive field ( E C ) of 2 kV/cm. Raman spectra of all compounds are performed and correlated well with the X-ray diffraction and dielectric measurement results.  相似文献   

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