Mobility of lithium ions in the crystal structure of lithium gadolinium molybdate LiGd(MoO4)(2)

Dielectric spectroscopy was used to show that, for LiGd(MoO4)(2), a complex molybdate with a stoichiometric oxygen content and a scheelite-type structure, the electric conduction in a wide temperature range mainly occurs via Lif ions. The dielectric relaxation in a c-axis-cut single crystal was studied over the temperature range 400-1000 K within the framework of the model of thermal ion jumps. This model yielded a minimum jump length for Li+ ions of 1.32 Angstrom and a height of the potential barrier between the nearest positions of ions of 1.65 eV, a value close to the conduction activation energy below the melting point of the crystal

Optical nonlinearity and dielectric properties of noncentrosymmetric crystals of RE borotungstate family Ln(3)BWO(9)

The second harmonic generation method was used to prove the noncentrosymmetric structure of Ln(3)BWO(9) borotungstates for elements of the RE series from lanthanum through gadolinium. The crystals exhibit moderate optical nonlinearity in the absence of phase matching between the radiation of the neodymium laser and its second harmonic. An increase in the optical nonlinearity in the middle of the RE series is caused by a more severe distortion of the WO6 polyhedra in crystals. In the range 500-800 K, Tb3BWO9 crystals exhibit dielectric relaxation, while at higher temperature, they are conductors of the Arrhenius type. Both phenomena were analyzed for the a- and c-cuts of Tb3BWO9 single crystals using the model of oxygen ion transfer over vacancies

Mobility of lithium ions in the crystal structure of lithium gadolinium molybdate LiGd(MoO4)(2)

Dielectric spectroscopy was used to show that, for LiGd(MoO4)(2), a complex molybdate with a stoichiometric oxygen content and a scheelite-type structure, the electric conduction in a wide temperature range mainly occurs via Lif ions. The dielectric relaxation in a c-axis-cut single crystal was studied over the temperature range 400-1000 K within the framework of the model of thermal ion jumps. This model yielded a minimum jump length for Li+ ions of 1.32 Angstrom and a height of the potential barrier between the nearest positions of ions of 1.65 eV, a value close to the conduction activation energy below the melting point of the crystal

Structural changes in Sr9In(PO4)7 during antiferroelectric phase transition

International audienceStructural changes in Sr9In(PO4)7 during the antiferroelectric (AFE) phase transition are studied by X-ray powder diffraction, electron microscopy, second-harmonic-generation, and dielectric measurements. Sr9In(PO4)7 complements a group of Ca3(VO4)2-type ferroelectric (FE) phosphates and vanadates and is the first example of an AFE material in this family. Antiparallel shifts of Sr atoms from their average positions and ordering of the P1O4 tetrahedra form two contributions in the structural mechanism of the AFE phase transition a displacive contribution and an order-disorder constituent, respectively. The displacive and order-disorder type of structural changes may account for the obtained value of the Curie-Weiss constant (C ~ 104 K) which is in between the value usually observed for pure displacive (C ~ 105 K) and that for orderdisorder phase transitions (C ~ 103 K). The structural mechanism of the AFE phase transition in Sr9In(PO4)7 is very similar to that of the FE phase transition in Ca9R(PO4)7 and Ca9R(VO4)7. Both displacive and orderdisorder contributions are responsible for the physical properties of the Ca3(VO4)2-type materials. © 2016 Pleiades Publishing, Ltd

Structural changes in Sr9In(PO4)7 during antiferroelectric phase transition

Structural changes in Sr9In(PO4)7 during the antiferroelectric (AFE) phase transition are studied by X-ray powder diffraction, electron microscopy, second-harmonic-generation, and dielectric measurements. Sr9In(PO4)7 complements a group of Ca3(VO4)2-type ferroelectric (FE) phosphates and vanadates and is the first example of an AFE material in this family. Antiparallel shifts of Sr atoms from their average positions and ordering of the P1O4 tetrahedra form two contributions in the structural mechanism of the AFE phase transition a displacive contribution and an order-disorder constituent, respectively. The displacive and order-disorder type of structural changes may account for the obtained value of the Curie-Weiss constant (C ~ 104 K) which is in between the value usually observed for pure displacive (C ~ 105 K) and that for orderdisorder phase transitions (C ~ 103 K). The structural mechanism of the AFE phase transition in Sr9In(PO4)7 is very similar to that of the FE phase transition in Ca9R(PO4)7 and Ca9R(VO4)7. Both displacive and orderdisorder contributions are responsible for the physical properties of the Ca3(VO4)2-type materials. © 2016 Pleiades Publishing, Ltd

Influence of NaCl/LiF Additives on Structure, Microstructure and Phase Transitions of (K0.5Na0.5)NbO3 Ceramics

Influence of NaCl/LiF additives (with molar ratio of 0.58:0.42) on phase formation, unit cell parameters, microstructure, dielectric and ferroelectric properties of (K0.5Na0.5)NbO3 ceramics has been studied. Intensification of the sintering process and a decrease in the unit cell parameters were proved. Enhancement of ferroelectric properties and an increase in the Curie temperature value stimulated by the additives were revealed using the Dielectric Spectroscopy and Second Harmonic Generation methods. © 2015 Copyright Taylor and Francis Group, LLC

Structure and ferroelectric properties of lead-free NBT-KBT-BF ceramics

Phase formation, crystal structure parameters, dielectric and ferroelectric properties of ceramic solid solutions in the (1-y)[(1-x)(Na0.5Bi0.5)TiO3-x(K0.5Bi0.5)TiO3]-yBiFeO3 system with x = 0.25, y = 0–0.6 has been studied. Pure samples with the pseudocubic perovskite structure were obtained by the solid state reaction method. Addition of BiFeO3 stimulated a monotonous increase in the unit cell volume and in the Curie temperature Tm value. With increasing the BiFeO3 content, nonmonotonous behaviour of the dielectric permittivity, a decrease in the Tph value, a decrease in total electroconductivity and dielectric loss at the room temperature were revealed. © 2017 Taylor & Francis Group, LLC

Composition dependence of the multifunctional properties of Nd-doped Bi4Ti3O12 ceramics

Sample preparation, evolution of the crystal structure with Nd content at room temperature, as well as dielectric and magnetic properties of polycrystalline Bi4 − xNdxTi3O12 solid solutions (x = 0.0, 0.5, 1.0, 1.5, and 2.0) are reported. These solid solutions were structurally characterized by X-ray powder diffraction using Rietveld refinements. For x ≤ 1.0, the samples crystallize in an orthorhombic symmetry. The structural data could be refined using the polar orthorhombic space group B2cb. The orthorhombicity decreases with increasing Nd3+ concentration, and a paraelectric tetragonal structure (space group I4/mmm) is stabilized for x > 1.The ferroelectric Curie temperature was found to monotonously decrease with increasing Nd concentration. A polar-to-nonpolar phase transition takes place near x = 1, reflecting the existence of a morphotropic phase boundary between 1.0 < x < 1.5 at room temperature. All samples were found to be paramagnetic down to 5 K, however, the presence of significant antiferromagnetic interaction is inferred from Curie–Weiss analyses of the temperature dependence of the magnetic susceptibility of the doped samples. The effect of Nd3+ substitution on structure–property relationship is discussed and compared to that of other lanthanide cations. © 2017, The Author(s)

Influence of NaCl/LiF Additives on Structure, Microstructure and Phase Transitions of (K0.5Na0.5)NbO3 Ceramics

Influence of NaCl/LiF additives (with molar ratio of 0.58:0.42) on phase formation, unit cell parameters, microstructure, dielectric and ferroelectric properties of (K0.5Na0.5)NbO3 ceramics has been studied. Intensification of the sintering process and a decrease in the unit cell parameters were proved. Enhancement of ferroelectric properties and an increase in the Curie temperature value stimulated by the additives were revealed using the Dielectric Spectroscopy and Second Harmonic Generation methods. © 2015 Copyright Taylor and Francis Group, LLC

Phase formation, structure and dielectric properties of lead-free ceramics on the base of (Na0.5Bi0.5)TiO3

The influence of BiFeO3 on phase formation, crystal structure, and dielectric properties of solid solutions close to the Morphotropic Phase Boundary in the (Na0.5Bi0.5)TiO3 - (K0.5Bi0.5)TiO3 system was studied. The formation of samples with pure perovskite structure was proved, increase in the unit cell parameters and in the Tm value while decrease in elelctroconductivity and dielectric loss stimulated by the BiFeO3 addition were revealed. © 2017 Taylor & Francis Group, LLC