Electrical Properties and Oxygen Stoichiometry of BaSrTiO Ceramics.

BaSrTiO solid solutions prepared by a solid-state reaction in air at 1200-1400 °C, followed by slow cooling to room temperature at the end of the reaction, were essentially oxygen-stoichiometric and p-type. Their conductivity increased reversibly when either p(O) in the surrounding atmosphere was increased or a dc bias as small as 1 V was applied across the samples. The enhanced p-type conductivity is attributed to the creation of mobile holes on underbonded oxide ions.

Field-enhanced bulk conductivity and resistive-switching in Ca-doped BiFeO3 ceramics.

The bulk conductivity at room temperature of Ca-doped BiFeO3 ceramics is p-type and increases reversibly by up to 3 orders of magnitude under the influence of a small dc bias voltage in the range ∼3 to 20 V mm(-1). The effect occurs in both grain and grain boundary regions, is isotropic and does not involve creation of filamentary conduction pathways. It is proposed that, by means of capacitive charging and internal ionisation processes under the action of a dc bias, hole creation leads to a more conductive excited state.

Hole conductivity in oxygen-excess BaTi1-xCaxO3-x+δ.

BaTiO3 containing Ca substituted for Ti as an acceptor dopant, with oxygen vacancies for charge compensation and processed in air, is a p-type semiconductor. The hole conductivity is attributed to uptake of a small amount of oxygen which ionises by means of electron transfer from lattice oxide ions, generating O(-) ions as the source of p-type semiconductivity. Samples heated in high pressure O2, up to 80 atm, absorb up to twice the amount expected from the oxygen vacancy concentration.

Synthesis, structural characterization, and electrical properties of new oxygen-deficient tetragonal tungsten bronzes Ba2NdTi(2+x)Nb(3-x)O(15-x/2).

Oxygen-deficient tetragonal tungsten bronzes ceramics with general formula Ba(2)NdTi(2+x)Nb(3-x)O(15-x/2) (0 ≤ x ≤ 1) have been prepared by low temperature solvothermal synthesis with final firing of ceramics at 1100-1300 °C in air. Rietveld refinement of X-ray powder diffraction (XRD) and neutron powder diffraction (ND) data at room temperature of Ba(2)NdTi(3)Nb(2)O(14.5) shows that Ba and Nd are ordered on the 15-coordinate and 12-coordinate sites, respectively, Ti and Nb are disordered nonrandomly over the two octahedral sites, and oxygen vacancies locate preferentially in the coordination sphere of Nd and Ti/Nb(2) atoms.