Synthesis and characterization of (Sr1−x′K2x)Zr4(PO4)6 ceramics

Single phase (Sr_1–x K_2x )Zr₄(PO₄)₆, where x lies between 0.0 and 1.0, ceramic powder with a submicron scale particle size has been synthesized successfully at calcination temperatures as low as 650–750°C by a sol-gel technique. The formation of the powder strongly depends on calcination temperature, but is independent of solution pH in the studied range. Dilatometric measurement shows an ultra-low linear coefficient of thermal expansion of 0.1×10^–6°C^–1 when x=0.5 at temperature intervals of 25–1000°C. Thermal conductivity and flexural strength of the materials were determined at ambient temperature to be 1.0 Wm^–1K^–1 and as high as 280 MPa, respectively, indicating that this material can be an excellent candidate in many applications, especially those subjected directly to severe environments.     

Synthesis and properties of TlIn1 − x Gd x Se2 solid solutions

This paper describes the synthesis and crystal growth of TlIn_{1 − x} Gd _x Se₂ solid solutions and presents the T-x phase diagram of the TlInSe₂-TlGdSe₂ system. Partial gadolinium substitution for indium in TlInSe₂ increases the microhardness and unit-cell parameters of the material and reduces its band gap. According to X-ray diffraction data for TlInSe₂-TlGdSe₂ crystals, the TlIn_{1 − x} Gd _x Se₂ (0 < x ≤ 0.1) solid solutions crystallize in tetragonal symmetry and are isostructural with TlInSe₂.     

Synthesis,microstructure and properties of (Ti1−x,Mox)2AlC phases

The reaction path of the (Ti_0.9, Mo_0.1)₂AlC phase from Ti, Al, TiC and Mo powder mixtures was investigated in detail ranging from 500 to 1450°C, and the results show that the reaction between Ti and Al produced Ti–Al intermetallics, and the reaction between Al and Mo formed Mo–Al intermetallics. And then the (Ti_0.9, Mo_0.1)₂AlC phase was formed by the reaction of Ti–Al, Mo–Al intermetallics, and TiC. At 1350°C for 2?h, a dense (Ti_0.9, Mo_0.1)₂AlC phase with purity was successfully fabricated. The Vickers hardness, flexural strength and fracture toughness were 5.48?GPa, 363.60?MPa and 5.78?MPa m^1/2, which were improved by 44, 34 and 136% for (Ti_0.80, Mo_0.20)₂AlC, respectively, compared with the single-phase Ti₂AlC.     

Synthesis,phase confirmation and electrical properties of (1 − x)KNNS−xBNZSH lead-free ceramics

Journal of Materials Science: Materials in Electronics - In the present work, lead-free piezoelectric ceramics (Rx)(K0.5Na0.5)(Nb0.96Sb0.04O3)?x(Bi0.5Na0.5)(Zr0.8Sn0.1Hf0.1)O3 [abb. as...     

Temperature dependence of elastic and dielectric properties of (Bi2O3)1 − x(CuO)x oxide glasses

Oxide glasses with the general formula (Bi₂O₃)_{1 - x}(CuO)_x have been prepared by quick quenching technique. Their longitudinal and shear elastic moduli have been determined by measuring the corresponding ultrasonic wave velocities between 300 and 470 K, which are well below the glass transition temperature of this system. Temperature variation of ultrasonic velocity and attenuation exhibit anomalies around 435 K in glasses with x 0.3. A nonlinear behaviour is also reflected in the CuO concentration dependent dielectric constant curve around x = 0.3. These anomalies are interpreted in terms of a structural softening (or transformation) taking place in samples having CuO concentration above the critical value. The high dielectric constant of these glasses show very little increase with increase of temperature. Anomalies are also found in the temperature dependence of dielectric constant around 435 K. This behaviour is again considered to be associated with the softening of the glass network.     

Sintering and properties of SrBi2(Ta1−x V x )2O9 ceramics

The effects of vanadium doping on the sintering, microstructure, dielectric properties, and ferroelectric properties of SrBi₂(Ta_1–x V _x )₂O₉ ceramics were investigated. The densification and grain-growth processes of the vanadium doped ceramics were shifted to a lower temperature range. For the ceramics with relative density 90%, the dielectric constant is 120–125 and 100–130 for the undoped and doped ceramics, respectively, and the dielectric loss tangent is below 1%. As compared with the undoped ceramics, the ferroelectric properties can be significantly improved by doping with an appropriate amount of vanadium and sintering at 1000°C. The variations of dielectric and ferroelectric properties are influenced by the incorporation of vanadium into crystal lattice and several microstructural factors.     

Dielectric and thermal properties of xPbTiO3-(1 − x)SrTiO3 Polycrystals

SrTiO₃ and PbTiO₃ perovskites are combined to form the xPbTiO₃-(1 – x)SrTiO₃ (PST) solid solution. In this work, a study of its dielectric and thermal properties is reported as a function of PbTiO₃ content. The dielectric properties of the xPbTiO₃-(1 – x)SrTiO₃ solid solution are determined through a thermoelectric analysis technique and hysteresis measurements. Such measurements made at room temperature for all compositions show the influence of one component upon the other resulting in a response to the electric field that involves a strained lattice behavior. A limiting case of antiferroelectric-like behavior is observed for x = 0.5. The thermal properties such as the specific heat capacity (c) and thermal diffusivity () were determined using a photoacoustic technique (PA) and the temperature relaxation method (TRM). The thermal conductivity was calculated from the results obtained for c and .     

Physical and electrical properties of MnO2-doped Pb(Zr x Ti1−x )O3 ceramics

The effects of composition on the physical property change in the phase coexistence region between the tetragonal and rhombohedral phases have been investigated as a function of zirconium concentration, x, for the MnO₂-doped Pb(Zr _x Ti_1–x )O₃ (0.40x0.60) ceramics. The relative amount of phase coexisting between the tetragonal and rhombohedral phases affects greatly both dielectric and piezoelectric properties as a function of zirconium concentration. However, there are no detectable changes between the apparent density and microstructure. Also, in the coexistence region, the relative amount of coexistence of the rhombohedral phase increases with MnO₂ addition. The inflection points of the dielectric constant shift to lower zirconium concentration in proportion to the MnO₂ addition, owing to the substitution effect on the PZT lattice site.     

Phase diagram and some properties of Cu2−xSe(2.01≥2−x≥1.75)

The temperatures of phase transformation from low-temperature -phase to high-temperature -phase were measured for copper selenide Cu_2–x Se in the composition range 2.012–x1.75. The -phase was found to be unstable in air, and further experiments should be performed in a good vacuum. The phase diagram of Cu_2–x Se was redetermined by the X-ray parametric method and the possible reasons why the phase diagrams reported by several authors do not coincide with each other are discussed.     

Synthesis and IR-excited luminescence of (Y1 − x Tm x )2O2S solid solutions

We have studied the key features of the luminescence spectra and kinetics of (Y_{1 ? x} Tm _x )₂O₂S solid solutions in the range 400–2000 nm under laser excitation at 790 and 810 nm. The results have been used to develop a series of IR phosphors “invisible” under laser excitation in the range 790–810 nm and possessing tunable and reproducible relative intensities of three groups of IR luminescence bands in the ranges 770–840, 1360–1520, and 1650–1980 nm, respectively.     

Microwave dielectric properties of Ba(Sn x Zn(1−x)/3Nb(1−x)2/3)O3 (0 ⩽ x ⩽ 0.32) ceramics

The dielectric properties of the (1–x)Ba(Zn_1/3Nb_2/3)O₃–xBaSnO₃ (0 x 0.32) composition at microwave frequencies were investigated in this study. With the addition of BaSnO₃, the dielectric Q(Q _d) value of Ba(Zn_1/3Nb_2/3)O₃ (BZN) can be improved and a small temperature coefficient of resonant frequency (_f) can be achieved. When 22.6 mol % of Sn is added to BZN, the characteristics of the Ba(Sn_0.226Zn_0.258Nb_0.516)O₃ ceramics sintered at 1500°C are as follows: dielectric constant _r = 32, _f = + 12 p.p.m.°C¹ and high Q _d value of 9700 at 10 GHz. Based on the classical dispersion theory and the logarithmic mixing rule, the effects with additions of substitutional element of BaSnO₃ on the microwave dielectric properties of Ba(Zn_1/3Nb_2/3)O₃ can be mostly explained.     

Crystalline structure and dielectric properties of (Sr1−1.5x Bi x ) TiO3 ceramics

The crystalline structure, microstructure and dielectric properties of the (Sr_1–1.5x Bi _x )TiO₃ (0 x 0.267) ceramics were studied. Cubic solid solutions were determined for x 0.2 at room temperature. However, lattice distortion was detected by Raman spectra. A dense microstructure with the grain sizes of 2–4 m was obtained for (Sr_1–1.5x Bi _x )TiO₃ (0 x 0.2) ceramics. The Bi concentration was examined and found to be in agreement with the nominal composition and overall uniformly distributed in the sample. Different from the observations in the earlier literature for other doped quantum paraelectrics, where only an induced dielectric anomaly was reported, there are three Bi induced dielectric modes A, B, and C in the Bi doped SrTiO₃ samples. The occurrence of the impurity modes and the ferroelectric relaxor mode and their evolution are demonstrated as a function of Bi concentration.     

Formation and properties of amorphous (Fe1−x Nb x ) l B100−l

Amorphous (Fe_1–x Nb _{x l} B_100–l alloys with 0 x 0.15 and 74 T _g, crystallization temperatureT _x, and microhardnessH _v, but to decrease the magnetization and Curie temperatureT _c. The effects of niobium onT _x,H _v, andT _c in iron-based amorphous alloys are similar to those of chromium, manganese, molybdenum, tungsten and vanadium.     

The evolution of structure and properties in GdMn(1−x)TixO3 ceramics

In this work, the effects of Ti doping on the microstructure, dielectric, and magnetic properties of GdMn_(1?x)Ti_xO₃ (x?=?0.00–0.15) ceramic samples synthesized using a solid-state reaction were investigated. All the experimental samples formed a single-phase structure, and no structural transformation occurred within the experimental doping range; however, Ti doping caused lattice shrinkage. Ti doping reduced the grain size, and the microstructure of the synthesized samples appeared more compact in scanning electron microscopy images. The lattice distortion of GdMn_(1?x)Ti_xO₃ caused by Ti substitution at the Mn sites resulted in changes in the Raman vibration modes. X-ray photoelectron spectroscopy results showed that the valence state transition of the Ti and Mn ions occurred and the concentration of Ti⁴⁺, Mn³⁺ ions and oxygen vacancies changed due to the charge compensation induced by Ti doping. Ti doping had a significant influence on the size and concentration of cation vacancies in the GdMn_(1?x)Ti_xO₃ samples. Appropriate Ti doping was shown to reduce the dielectric loss, improve the frequency stability of the dielectric constant, and significantly affect the long-range ordering of Gd³⁺ magnetic moments and clearly reduce magnetization.

     

Synthesis and electrical properties of (BaTiO3)1 ?x (K0.5Bi0.5TiO3) x solid solutions

(BaTiO₃)_{1 ? x} (K_0.5Bi_0.5TiO₃) _x solid solutions exhibiting positive temperature coefficient of resistance behavior have been prepared using BaTiO₃ presynthesized through oxalate coprecipitation. The peak in their dielectric permittivity has been shown to shift to higher temperatures (above 120°C) with increasing x. We have examined the effect of K_0.5Bi_0.5TiO₃ content on the microstructure of the (BaTiO₃)_{1 ? x} (K_0.5Bi_0.5TiO₃) _x solid solutions. The results demonstrate that, with increasing x, both the minimum and maximum resistivities of the materials in the temperature range of their positive temperature coefficient of resistance behavior increase. The materials prepared using barium titanate presynthesized by the oxalate route have higher Curie temperatures and temperatures where they exhibit positive temperature coefficient of resistance behavior and lower minimum resistivities than do the materials prepared by solid-state reactions.     

Color tunning and temperature-dependent photoluminescence properties of Sr0.3Ca0.7−x−y(MoO4)2: xDy3+, yEu3+

Journal of Materials Science: Materials in Electronics - A series of Sr0.3Ca0.7?x?y(MoO4)2: xDy3+, yEu3+ phosphors with a tunable color was prepared by the conventional co-precipitation...