M. Dambekalne

The formation process of complex lead-containing niobates

Abstract The sequence of phases formed during the solid state reaction in oxide mixtures from 500 to 900°C has been studied by x-ray diffraction in ternary system PbO:Nb2O5:X, where X = MgO, ZnO, Sc2O3 or In2O3. The following compositions have been investigated: 3PbO:2Nb2O5:X, 2PbO:Nb2O5:X, 5PbO:2Nb2O5:X, 3PbO:Nb2O5:X and 4PbO:Nb2O5:X, the concentration of X phase being taken from 0 to 1.2 molar parts. The perovskite structure Pb(Mg1/3Nb2/3)O3, Pb(Sc1/2Nb1/2)O3, Pb(In1/2Nb1/2)O3 is found to be formed in a complicated multistage process with several intermediate products during the reaction. The end product is sintered at temperatures beyond 800°C in a reaction between two phases with a pyrochlore structure: Pb5·Nb4O15 and Pb3Nb2O8. The diagrams of forming the end products during reactions (perovskite and pyrochlore—cubic) are proposed.

Production of complex lead-containing niobates transparent ferroelectric ceramics

The sequence of phases formed during the solid state reaction in oxide mixtures has been studied by X-ray diffraction and differential thermal analysis (DTA) in the binary oxide system PbO-Nb2, O5 and the ternary oxide system PbO-Nb2O5-Sc2O3. The following compositions have been investigated: 3PbO : 2Nb2O5, 2PbO : Nb2O5, 5PbO : 2Nb2O5, 3PbO : Nb2O5, 4PbO : Nb2O5, and 3PbO : 2Nb2O5 : X, 2PbO : Nb2O5 : X, 5PbO : 2Nb2O5 : X, 3PbO : Nb2O5 : X, 4PbO: Nb2O5 : X, the molar ratio X of Sc2O3 being taken 0; 0.025; 0.05; 0.1; 0.3; 0.5; 0.8; 1.0; 1.2.It is found that the formation of both the binary and ternary compounds includes complicated multistage processes with several intermediate products during the reaction. In all cases, except 3PbO : 2Nb2O5, one or more additional phases less rich in lead oxide coexist with the stoichiometric phase. Obviously, this is due to evaporation of lead oxide above 800°C. Therefore PbSc1/2Nb1/2O3, produced from the stoichiometric proportion of oxides 4PbO : Nb2O5 : Sc2O3 by a solid...

Production and properties of ceramics of lead containing niobates

Abstract Ceramic solid solutions of PbMg1/3Nb2/3O3-PbSc1/2Nb1/2O3 (PMN-PSN) and PhZn1/3Nb2/3O3-PhSc1/2Nb1/2O3 (PZN-PSN) have been obtained as a single phase compositions of perovskite structure amount of pyrochlore phase being less than 5%. Only the hot pressed solid solution compositions appear to be transparent (transmittance of 50% in the case of best specimens). Ceramic, dielectric, piezoelectric and electrooptical properties have been measured and DTA, X-ray diffraction and microstructure examined. Solid solutions of PMN-PSN are completely soluble in each other and limited for PZN-PSN. It is not possible to obtain PZN and solid solutions with more than 0.6 mol. ratio of PZN. It contain the pyrochlore phase or mainly consists of that.

LEAD-FREE (Na0.5Bi0.5)1-xBaxTiO3 SINGLE CRYSTALS (0 ≤ x ≤ 0.05) AND THEIR DIELECTRIC AND PYROELECTRIC PROPERTIES

ABSTRACT Lead-free single crystals of Na0.5Bi0.5TiO3-BaTiO3 (NBT-BT) system were prepared by Czochralski method and their dielectric and pyroelectric properties have been studied. The results were compared with these for pure NBT. The obtained samples show pure perovskite structure with rhombohedral symmetry at room temperature. Low frequency (100 Hz–100 kHz) investigations reveal the diffuse phase transitions. The obtained results are discussed in terms of local electric and strain fields caused by different ionic radius of (Na, Bi) and Ba ions. The NBT-BT system is expected to be a new promising candidate for lead-free electronic crystals.

SYNTHESIS AND CHARACTERIZATION OF SB-SUBSTITUTED (K0.5Na0.5)NbO3 PIEZOELECTRIC CERAMICS

ABSTRACT Lead-free piezoelectric ceramics (K0.5Na0.5)(Nb1-xSbx)O3+0.5 mol.%MnO2, where x = 0 ÷ 0.10, with single phase structure and rhombohedral symmetry at room temperature were prepared by conventional ceramic technology. The optimal sintering temperatures of compositions were within 1100°–1140°C. MnO2 functions as a sintering aid and effectively improves the densification. The samples reached density from 4.26 g/cm3 for undoped (K0.5Na0.5)NbO3 to 4.40 g/cm3 for Mn/Sb5+ co-doped ceramics. The co-effects of MnO2 doping and Sb5+ substitution lead to significant improvement in dielectric and piezoelectric properties: ϵ at the Tc increased from 6000 (KNN) to 12400 (x = 0.04), d33 = 92 ÷ 192 pC/N, kp = 0.32 ÷ 0.46, kt = 0.34 ÷ 0.48.

SINTERING OF LEAD-FREE (K0.5Na0.5)NbO3 BASED SOLID SOLUTION

ABSTRACT In this study lead-free solid solution (K0.5Na0.5)NbO3 was prepared, structure, dielectric parameters of ceramics were investigated. The doping of sintering aids did not affect the crystallographic structure of the ceramics significantly; all ceramic samples had a single-phase perovskite structure. Added elements CdO, ZnO, MnO2, V2O5 effectively decreased the sintering temperature of KNN by 50°–80°C. All sintering aids influenced sinterability, microstructure and dielectric properties of ceramics. Dielectric constant for doped samples increased from 6000 up to 8000; Pr = 15 μC/cm2, Ec = 9 kV/cm, d33 = 110 pC/N, kp = 0.38 and Qm = 190 for MnO2 doped samples.

Effect of compressive stress on dielectric and ferroelectric properties of 0.25PSN-0.75PLuN ceramics

The PSN-PLuN solid solutions have been prepared in the whole composition range for the first time. The dielectric, pyroelectric and hysteresis loops measurements of the 0.25PSN-0.75PLuN ceramics stress-free or under the stress (0-1.5 kbar) have been carried out. It is found that compressive stress shifts the phase transformation and decrease the field-polarization hysteresis. These effects can be mainly connected with the change in domain walls dynamics and with polarization switching under the action of stress.

DIELECTRIC PROPERTIES OF LEAD-FREE [(1-x)(Na0.5Bi0.5)-xBa]Zr1−y Ti y O3 CERAMICS (x = 0.01, 0.06, 0.085, 0.09, 0.1 AND y = 0.96, 0.97)

ABSTRACT Lead-free ceramics based on (Na0.5Bi0.5TiO3, NBT)-(Ba(Ti, Zr)O3, BTZ) were prepared by solid phase synthesis and hot pressing sintering process and their dielectric properties have been studied. The obtained results were compared with these for pure NBT. The obtained samples show pure perovskite structure. Low frequency (100 Hz-100 kHz) investigations reveal the diffuse phase transitions and relaxorlike behaviour. The obtained results are discussed in terms of inhomogeneity of ions distribution, their ferro- and antiferroactivity and internal stresses. The NBT-BTZ system is expected to be a new promising candidate for lead-free electronic ceramics.

Electrical Transport in Lead-Free [(1−x)(Na0.5Bi0.5)-xBa]Zr1 - yTiyO3 Ceramics (x = 0, 0.06, and y = 0, 0.96)

Lead-free ceramics based on (Na 0.5 Bi 0.5 TiO 3 , NBT)-(Ba(Ti,Zr)O 3 , BTZ) were prepared by solid phase hot pressing sintering process and their ac (σ ac ) and dc (σ dc ) conductivity have been studied (303–753 K). Low frequency (100 Hz–100 kHz) ac conductivity obeys power law σ ac ∼ ω s characteristic for disordered materials. The frequency exponent s is a decreasing function of temperature and tends to zero at high temperatures. Dc conductivity has thermally activated character and possesses four linear parts with four different activation energies and some discontinous changes. However, σ ac (T) possesses two linear parts with two different activation energies and more discontinuous changes than dc conductivity. The results was interpreted by correlated hopping model. The NBT-BTZ system is expected to be a new promising candidate for lead-free electronic ceramics.

New ferroelectric materials on the basis of PbSc1/2Nb1/2O3–PbLu1/2Nb1/2O3 solid solutions

Abstract Original binary solid solutions PbSc 1/2 Nb 1/2 O 3 –PbLu 1/2 Nb 1/2 O 3 (PSN-PLuN) have been produced. First of all nominally pure PSN and PLuN were synthesized by solid state reaction from oxides and carbonates. These compounds were mixed in different proportions to obtain (1− x )PSN− x PLuN solid solutions. Ceramic samples were hot-pressed at gradual change of the temperature. Solid solutions have the perovskite structure and are completely soluble in each other. Differential thermal analysis and X-ray diffraction were used to examine the synthesis and phase constitution. Dielectric properties—dielectric permittivity e and dielectric loss tan δ of ceramic samples of originally synthesized PbSc 1/2 Nb 1/2 O 3 –PbLu 1/2 Nb 1/2 O 3 (PSN−PLuN) solid solution series were measured as functions of temperature. In (1− x )PSN− x PLuN solid solutions the phase transition temperature drops at small values x further proceeding through a minimum.