Oxygen non-stoichiometry determination of perovskite materials by a carbonation process

A new and easy method is developed to determine the oxygen non-stoichiometry of perovskite materials under equilibrium conditions. The method is based on the complete decomposition of the powder to stoichiometric metal oxides and/or metal carbonates by using CO2 as reacting gas. The oxygen non-stoichiometry is calculated from the mass change caused by this reaction. Its applicability is demonstrated by using SrCoO3 − δ, BaCoO3 − δ, BaFeO3 − δ and BaCeO3 − δ as representative materials. The oxygen non-stoichiometry (δ) values at 950 °C in air were determined as 0.48, 0.36, 0.43 and 0.03 respectively. These values can be used as reference points for oxygen non-stoichiometry analysis at other temperature

Grain growth in ultrafine-grained Y-TZP ceramics

Grain growth in dense ultrafine-grained (120–600 nm) tetragonal ZrO2-Y2O3 ceramics is studied as a function of temperature. At all temperatures investigated both segregation and phase partitioning occur. It is argued that at temperatures ≤ 1150 °C grain growth is not significantly inhibited by solid solution drag or by phase partitioning. At higher temperatures the grain growth behaviour can be explained by the models of solid solution drag and/or phase partitioning depending on conditions.\u

A hydrothermal route for production of dense, nanostructured Y-TZP

Y-TZP powders were prepared either by calcination in air or crystallization under hydrothermal conditions of a hydrous gel, obtained by coprecipitation. Differences in powder properties, green compact structure and sinterability were examined. Crystallization under hydrothermal conditions occurs at temperatures as low as 190°C in the presence of ammonia. The hydrothermally treated powders are composed of soft agglomerates, that collapse under very low pressures, resulting in green bodies with high densities and small pore radii. The sinterability is greatly improved by the hydrothermal treatment and allowed the production of dense, nanostructured Y-TZP by free sintering at 1050°C

Analysis of reactions during sintering of CuO-doped 3Y-TZP nano-powder composites

3Y-TZP (yttria-doped tetragonal zirconia) and CuO nano powders were prepared by co-precipitation and copper oxalate complexation–precipitation techniques, respectively. During sintering of powder compacts (8 mol% CuO-doped 3Y-TZP) of this two-phase system several solid-state reactions clearly influence densification behaviour. These reactions were analysed by several techniques like XPS, DSC/TGA and high-temperature XRD. A strong dissolution of CuO in the 3Y-TZP matrix occurs below 600 °C, resulting in significant enrichment of CuO in a 3Y-TZP grain-boundary layer with a thickness of several nanometres. This “transient” liquid phase strongly enhances densification. Around 860 °C a solid-state reaction between CuO and yttria as segregated to the 3Y-TZP grain boundaries occurs, forming Y2Cu2O5. This solid-state reaction induces the formation of the thermodynamic stable monoclinic zirconia phase. The formation of this solid phase also retards densification. Using this knowledge of microstructural development during sintering it was possible to obtain a dense nano–nano composite with a grain size of only 120 nm after sintering at 960 °C

Characterization of Grain Boundaries in Superplastically Deformed Y-TZP Ceramics

The effects of compressive deformation on the grain boundary characteristics of fine-grained Y-TZP have been investigated using surface spectroscopy, impedance analysis, and transmission electron microscopy. After sintering at low temperature (1150°C), the grain boundaries are covered by an ultrathin (1nm) yttrium-rich amorphous film. After deformation at 1200°–1300°C under low stress, some grain boundaries are no longer covered by the amorphous film. Yttrium segregation seems to occur only at wetted grain boundaries. Evidence has been found that the extent of dewetting increases with increasing applied stress

Effect of annealing in O2 or N2 on the aging of Fe0.5Mn1.84Ni0.66O4 NTC-ceramics

Fe0.5Mn1.84Ni0.66O4 NTC ceramic thermistors were annealed in nitrogen or oxygen atmosphere at 600 °C. The change of the electrical properties of the thermistors with time was reduced sharply by annealing in N2, whereas it was enhanced upon annealing in O2. N2-annealed samples exhibited a less degree of redistribution of cations in the lattice as compared with O2-annealed samples. The aging of the electrical properties is believed to result from the cation redistribution which in turn is favoured by the presence of cation vacancies. And the improved aging behaviour of the N2-annealed thermistor is explained by the reduction of the concentration of the cation vacancy upon annealing under lower oxygen partial pressure and the suppression of cation redistribution

Synthesis and characteristics of nanocrystalline 3Y-TZP and CuO powders for ceramic composites

A weakly agglomerated 3Y-TZP powder with 100% tetragonal crystal structure and a primary crystallite diameter of 8 nm was prepared by co-precipitation of metal chlorides in an ammonia solution, followed by extensive washing with ethanol, drying and calcining at 550 °C. Powder characteristics as function of thermal treatment are discussed. A copper oxalate precipitation for the preparation of nanocrystalline CuO powders was optimised in order to minimise aggregation and agglomeration. The influence of calcination procedure and synthesis medium on several powder characteristics of the CuO powders were investigated in detail. Oxalate precipitation in ethanol followed by sequential drying and calcination in air at 250 °C in an open tubular furnace with proper air-powder contact area was found to be the optimal procedure for producing nanocrystalline single-phase CuO powder with small aggregates and weak agglomerates. With this optimal procedure a CuO powder with crystallite diameter and BET equivalent particle diameter of respectively 12 and 20 nm was obtained

A novel method for the fabrication of freestanding PZT features on substrates

A simple and cheap micromoulding fabrication route was developed to prepare freestanding piezo active features. Dimensions as small as 200 μm by 200 μm and 40 μm high were successfully fabricated via a replication technique. The lead zirconate titanate features were thoroughly characterized using SEM, EDX and XRD analysis. The properties of the features were influenced by several factors like the type of substrate, sintering temperature and sintering atmosphere. Features prepared on alumina substrates and sintered in lead atmosphere displayed a structure with reproducible dimensions. Next to that they were low in porosity and had a comparable composition with respect to the starting powder. The remanent polarization of the lead zirconate film was 12.3 μC/cm2 and the coercive field was 8.7 kV/cm