Dielectric characteristics of La-modified PbTiO3 nanoceramics

The nanoceramics of lanthanum (La³⁺)-modified lead titanate (PbTiO₃) with a general formula Pb_1?yLa_yTi_(1?y/4)O₃ (y = 0.00, 0.06, 0.08, 0.10, 0.12 Lead Lanthanum Titanate (PLT)) were synthesized by a mechanothermal method. Thermal analysis of the PLT samples exhibits their nature of the reaction and thermal stability. The incorporation of La at the Pb site of lead titanate (PT) not only changes the ratios of its unit cell parameters but also reduces the grain and particle size to nanoscale. The dielectric constant of PLT is dependent on La concentration. The La concentration-dependent phase transition temperature of PbTiO₃ is one of the main characteristics of the material.     

Effect of heat treatment on pore structure in nanocrystalline NiO: A small angle neutron scattering study

Nanocrystalline nickel oxide powders were calcined at 300, 600 and 900°C and pore structure evolution was followed by small angle neutron scattering (SANS). Pore size distributions at two widely separated size ranges have been revealed. Shrinkage of larger-sized pore with reduction in polydispersity has been observed with increasing heat treatment temperature. The pore structures at various heat treatment temperatures do not scale. This has been attributed to the grain boundary diffusion leading to an asymmetric shrinkage of the pores.      

Transport properties, specific heat and thermal conductivity of GaN nanocrystalline ceramic

The structural and transport properties (resistivity, thermopower and Hall effect), specific heat and thermal conductivity have been measured for GaN nanocrystalline ceramic prepared by hot pressing. It was found that the temperature dependence of resistivity in temperature range 10-300 K shows the very low activation energy, which is ascribed to the shallow donor doping originating in amorphous phase of sample. The major charge carriers are electrons, what is indicated by negative sign of Hall constant and Seebeck coefficient. The thermopower attains large values (−58 μV/K at 300 K) and was characterized by linear temperature dependence which suggests the diffusion as a major contribution to Seebeck effect. The high electron concentration of 1.3×10¹⁹ cm⁻³ and high electronic specific heat coefficient determined to be 2.4 mJ/molK² allow to conclude that GaN ceramic demonstrates the semimetallic-like behavior accompanied by very small mobility of electrons (∼0.1 cm²/V s) which is responsible for its high resistivity. A low heat conductivity of GaN ceramics is associated with partial amorphous phase of GaN grains due to high pressure sintering.     

Microstructure and electrical transport in nano-grain sized Ce0.9Gd0.1O2−δ ceramics

An enhancement of the electrical conductivity has been found in nano-grain sized Ce_0.9Gd_0.1O_2−δ ceramics when measured in N₂ (p_O2=3.5×10⁻⁶ atm) in comparison with the most commonly accepted values of bulk ionic conductivity. We first present the synthesis and characterisation of the nanoparticles later used for the preparation of dense nanoceramics of Gd-doped CeO₂. The nanoparticles were characterised by X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The good sintering properties of these nanopowders allowed us to obtain very dense ceramics (>90% theoretical density) while keeping the grain size close to 100 nm. The microstructure of these nanoceramics was analysed by AFM and scanning electron microscopy (SEM) while the electrical characterisation was performed by the 4-point dc technique between 500 and 950 °C in air or N₂ and ac impedance between 150 and 400 °C in air and or argon. We briefly discuss the possibilities of electron vs. oxygen ion conduction and grain boundary vs. bulk conductivity. The features exhibited by these ceramics represent an increased potential to process solid electroceramics materials with specific levels of electronic and/or ionic conductivities for a variety of electrochemical devices.