Eliminating The Negative Effect Of Monoclinic Nb2O5 On Electrical Properties Of (K0.5Na0.5)Nbo3 Ceramics By Two-Step Sintering

This study investigates the electrical properties of (K0.5Na0.5)NbO3 (KNN) lead-free piezoelectric ceramics prepared by using monoclinic Nb2O5 as the starting material. The results reveal that the samples prepared by two-step sintering procedure are much better than those prepared by conventional sintering procedure. The piezoelectric constant (d33) reaches the value measured from the samples prepared from orthorhombic Nb2O5, suggesting the two-step sintering procedure could be an effective method to remove the negative effect of monoclinic Nb2O5. The underlying mechanism for the improving effect is discussed

Making Nanostructured Ceramics From Micrometer-Sized Powders Via Grain Refinement During Sps Sintering

In this paper, we have demonstrated that dense bulk nanostructured ceramics can be synthesized from micrometer-sized powders by using an electrical field-activated sintering process. A dense Pb(Mg1/3Nb 2/3)O3-PbTiO3 ceramic with grain sizes of 20-100 nm was obtained from the starting powder of 1 to 10 μm. Structural and property analysis confirmed that the entire specimen is composed of nano-sized grains. The significant microstructural refining is attributed to a pulsed electric field-induced thermo-mechanical fatigue process, which in situ shattered the large particles into nano-sized grains during sintering. An advantage of this technique over the previous ones is that it avoids the usage of ultrafine nanometer-sized powders, which are difficult to process and mass produce in an economic and consistent way. In principle, the process demonstrated here can be applied to other material systems. © 2008 The American Ceramic Society

Grain Refining In Spark Plasma Sintering Al2O3 Ceramics

The paper reports the effect of starting powder size and sintering temperature on the grain refining in spark plasma sintering Al2O3. It was found that the grain refining effect only occurred for the starting particles larger than a certain size. The grain size increased with increasing sintering temperature. The grain refining is likely caused by the rearrangement of dislocations through a thermo-mechanical fatigue process. It suggested that nanostructured alumina ceramics could be synthesized from micro-sized powders by optimizing the particle size and sintering temperature

A Five-Component Entropy-Stabilized Fluorite Oxide

In this paper, we report a new entropy-stabilized fluorite oxide, formed by solid-state reacting the equimolar mixture of CeO2, ZrO2, HfO2, TiO2 and SnO2 at 1500 °C. We demonstrated that the oxide is truly entropy-stabilized by showing that the oxide was transferred to a multiphase state when annealed at lower temperatures, and the transition between the low-temperature multiphase and high-temperature single-phase states is reversible. Room-temperature thermal conductivity of the fluorite oxide was measured to be 1.28 Wm−1 K−1. The value is only half of that for 7 wt% yttria-stabilized zirconia, suggesting the material could be useful for thermal-insulation applications

Screening Sintering Aids For (K0.5Na0.5)Nbo3 Ceramics

Searching for suitable sintering aids for ceramic materials is important and tedious work. In this study, we introduce a simple and effective method, named liquid phase screening method (LPSM), for rapidly screening sintering aids for KNN ceramics. By measuring the structure and properties, we demonstrated that the suitable sintering aids for KNN can be quickly determined by LPSM. The new sintering aids found by this method, GeO2 and borax which have not been reported before, lead to improved properties

Effects Of Geo2 Addition On Sintering And Properties Of (K0.5Na0.5)Nbo3 Ceramics

Lead-free (K0.5Na0.5)NbO3 (KNN) piezoelectric ceramics doped with different amounts of GeO2 were prepared and characterized. GeO2 was found to effectively improve the sinterability and piezoelectric properties of the material. The improvement in the sinterability is ascribed to the formation of a liquid phase, which decreased the sintering temperature from 1080°C to 1010°C. The improvement in the properties is attributed to the replacement of Nb5+ with Ge4+ to form acceptor dopants. The following optimized properties were obtained from the KNN ceramic with 0.75 wt% GeO2: piezoelectric constant (d33) = 126 pC/N, planar electromechanical coupling coefficient (kp) = 42.8%, mechanical quality factor (Qm) = 140, and dielectric loss (tanδ) = 3.8%

Fabrication And Properties Of Porous Anorthite Ceramics With Modelling Pore Structure

A single-phased anorthite porous ceramics was fabricated by foam-gelcasting technique using α-Al2O3, CaCO3 and SiO2 as starting material. Through adjusting foaming agent concentration and solid content in the slurry, tailored porosity (62–91%), pore size (7–350 μm), thermal conductivity (0.04–0.27 W/m·K) and compressive strength (0.27–13.39 MPa) were obtained. The experimental thermal conductivity was in good agreement with the universal model. The dependence of compressive strength on porosity can be described by the Gibson model

Acceptor Doping Effects In (K0.5Na0.5)Nbo3 Lead-Free Piezoelectric Ceramics

In this paper, the effects of acceptor dopants on the synthesis, sintering and properties of KNN ceramics were studied for (K0.5Na0.5)(Nb0.994A0.006)O3-δ (A=Ge4+, Ga3+, Zn2+, Mn2+, Ni2+, and Cu2+) ceramics. The results reveal that the eutectic phase(s) is (are) formed between the acceptor oxide and alkali metal carbonate, thereby significantly improving the sinterability of the materials. Compared to the trivalent and tetravalent acceptor dopants, divalent dopant can lead to higher Qm values, most likely due to the formation of defect complexes

Non-Contact Electric Field-Enhanced Abnormal Grain Growth In (K0.5Na0.5)Nbo3 Ceramics

The effect of a non-contact electric field on the sintering behavior of (K0.5Na0.5)NbO3 (KNN) ceramics was studied. The results revealed that the electric field can enhance the densification and grain growth, and promote abnormal grain growth in KNN ceramics. The phenomena are likely because the electric field promoted the formation of liquid phase, leading to enhanced mass transport. A simple thermodynamic model was proposed to explain the solid-liquid phase transformation under an electric field