Influence of Non-Stoichiometry on the Structure and Properties of Ba(Zn\u3csub\u3e1/3\u3c/sub\u3eNb\u3csub\u3e2/3\u3c/sub\u3e)O\u3csub\u3e3\u3c/sub\u3e Microwave Dielectrics: II. Compositional Variations in Pure BZN

The formation of non-stoichiometric cubic perovskite solid solutions based on BaZn1/3Nb2/3O3 (BZN) was examined along 10 different directions in the BaO–ZnO–Nb2O5 ternary system. Limited ranges of non-stoichiometry were observed along several pseudo-binaries and the BZN structure can accommodate a variety of different types of defects. Although the deviations from stoichiometry are quite small, typically ~1 mole%, they induce large changes in the extent and stability of the 1:2 B-site ordering, the sintering and microstructure, and the dielectric loss properties. The highest Q×fs (~110 000 at 8 GHz) in the system, which coincide with the highest degree of order, were located in two regions along the BZN–Ba5Nb4O15 and BZN–BaNb2O6 lines. The results of this study provide an explanation for the large variations in crystal structure and Q×fs previously reported for BZN and other related systems (e.g., Ba(Zn1/3Ta2/3)O3), and demonstrate that non-stoichiometric starting compositions provide a route to the highest Q values

Influence of Cation Order on the Dielectric Properties of Pb(Mg\u3csub\u3e1/3\u3c/sub\u3eNb\u3csub\u3e2/3\u3c/sub\u3e)O\u3csub\u3e3\u3c/sub\u3e-Pb(Sc\u3csub\u3e1/2\u3c/sub\u3eNb\u3csub\u3e1/2\u3c/sub\u3e)O\u3csub\u3e3\u3c/sub\u3e (PMN-PSN) Relaxor Ferroelectrics

The effect of the B-site cation chemistry and ordering on the dielectric properties of solid solutions in the (1-x)Pb(Mg1/3Nb2/3)O3-Pb(Sc1/2Nb1/2)O3 (PMN-PSN) perovskite system was examined in samples with 0.1 ≤ x ≤ 0.9. Thermal annealing treatments were effective in inducing long-range B-site order in the samples within this compositional range. The well-ordered, large chemical domain ceramics exhibit relaxor behavior up to x = ~0.5; for higher values of x, normal ferroelectric behavior was observed. For x ≤ 0.5 reductions in the chemical domain, size had no significant effect on the weak-field dielectric properties, but induced a transition to relaxor behavior for x \u3e ~0.6. The disordered PSN-rich samples undergo a spontaneous zero-field relaxor to ferroelectric transition similar to that reported previously for PSN. The field-dependent properties of compositions lying closest to the relaxor to ferroelectric crossover exhibited the highest sensitivity to alterations in the chemical order. The properties of this system are consistent with a random site description of the 1:1 ordered Pb(β′1/2 β1/2)O3 structure with β′ = (Mg(2-2x)/3Nb(1-x)/3Scx) and β″ = Nb

Ba\u3csub\u3e8\u3c/sub\u3eZnTa\u3csub\u3e6\u3c/sub\u3eO\u3csub\u3e24\u3c/sub\u3e: A New High Q Dielectric Perovskite

The hexagonal perovskite, Ba8ZnTa6O24, was prepared in single-phase form and was found to be a stable secondary phase, formed as a result of the loss of ZnO from Ba(Zn1/3Ta2/3)O3 microwave dielectrics. The experimental and calculated X-ray patterns of Ba8ZnTa6O24 indicate it is isostructural with Ba8Ta6NiO24 with an 8H (cchc)2 close-packed BaO3 stacking sequence and the lattice parameters, a=10.0825(14), c=19.0587 (38)Å . High-density ceramics of Ba8ZnTa6O24 could be prepared at temperatures considerably lower (1400ºC) than those used to sinter pure Ba(Zn1/3Ta2/3)O3, and exhibit very good microwave dielectric properties with ε=30.5, Qf=62300, and τf=+36 ppm/ºC at 8.9 GHz

A-Site and B-Site Order in (Na\u3csub\u3e1/2\u3c/sub\u3eLa\u3csub\u3e1/2\u3c/sub\u3e)(Mg\u3csub\u3e1/3\u3c/sub\u3eNb\u3csub\u3e2/3\u3c/sub\u3e)O\u3csub\u3e3\u3c/sub\u3e Perovskite

(Na1/2La1/2)(Mg1/3Nb2/3)O3 undergoes a series of phase transitions that involve cation order on the A- and B-sites of the parent perovskite structure. At high temperatures both sites contain a random distribution of cations; below 1275°C a 〈111〉 layering of Mg and Nb leads to the formation of a 1:2 ordered structure with a monoclinic supercell. A second transition was observed at 925°C, where the Na and La cations order onto alternate A-site positions along the 〈001〉 direction of the parent subcell. By quenching samples from above 1275°C to preserve the disorder on the B-site, a fourth variant of this compound was obtained by inducing A-site order through a subsequent anneal at 900°C. Although the changes in structure do not produce significant alterations in the relative permittivity (εr ~ 35), they do have a significant effect on the value of the temperature coefficient of the capacitance

Synthesis and Dielectric Properties of Li\u3csub\u3e1-\u3ci\u3ex+y\u3c/i\u3e\u3c/sub\u3eTa\u3csub\u3e1-\u3ci\u3ex\u3c/i\u3e-3\u3ci\u3ey\u3c/i\u3e\u3c/sub\u3eTi\u3csub\u3e\u3ci\u3ex\u3c/i\u3e+4\u3ci\u3ey\u3c/i\u3e\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e \u3ci\u3eM\u3c/i\u3e-Phase Solid Solutions

The synthesis, structure, and dielectric properties of the so-called M-phase solid solutions in the Li2O-Ta2O5-TiO2 system were investigated. Although the range of stability of the tantalate phases is more limited compared with their niobate counterparts, they have identical structures based on intergrowths of LiTaO3-type blocks separated by corundum type layers. The dielectric constants of the tantalate M-phases range from 68 to 52 and they all exhibit a negative temperature coefficient of capacitance. The temperature coefficient of the resonant frequency measured in the microwave region can be tuned to zero, and the system shows quite good quality factors with the highest value reaching a Q x f = 10500 at 6.7 GHz

Structure and Dielectric Properties of the Ba(Mg\u3csub\u3e1/3\u3c/sub\u3eNb\u3csub\u3e2/3\u3c/sub\u3e)O\u3csub\u3e3\u3c/sub\u3e–La(Mg\u3csub\u3e2/3\u3c/sub\u3eNb\u3csub\u3e1/3\u3c/sub\u3e)O\u3csub\u3e3\u3c/sub\u3e System

A complete range of perovskite solid solutions can be formed in the (1 - x)Ba(Mg1/3Nb2/3)O3–xLa(Mg2/3Nb1/3)O3 (BMN–LMN) pseudobinary system. While pure BMN adopts a 1:2 cation ordered structure, 1:1 ordered phases are stabilized for 0.05 ≤ x ≤ 1.0. Dark-field TEM images indicate that the La-doped solid solutions are comprised of large 1:1 ordered domains and no evidence was found for a phase-separated structure. This observation coupled with the systematic variations in the intensities of the supercell reflections supports a charge-balanced random-site model for the 1:1 ordering. The substitution of La also induces a transformation from a negative to positive temperature coefficient of capacitance in the region 0.25 ≤ x ≤ 0.5

Effect of V\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e5\u3c/sub\u3e Doping on the Sintering and Dielectric Properties of \u3ci\u3eM\u3c/i\u3e-Phase Li\u3csub\u3e1+x-y\u3c/sub\u3eNb\u3csub\u3e1-x-3y\u3c/sub\u3eTi\u3csub\u3ex+4y\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e Ceramics

The effect of the addition of V2O5 on the structure, sintering and dielectric properties of M-phase (Li1+x-yNb1-x-3yTix+4y)O3 ceramics has been investigated. Homogeneous substitution of V5+ for Nb5+ was obtained in LiNb0.6(1-x) V0.6xTi0.5O3 for x ≤ 0.02. The addition of V2O5 led to a large reduction in the sintering temperature and samples with x = 0.02 could be fully densified at 900oC. The substitution of vanadia had a relatively minor adverse effect on the microwave dielectric properties of the M-phase system and the x = 0.02 ceramics had εr = 66, Q x f = 3800 at 5.6 GHz, and τf = 11 ppm/oC. Preliminary investigations suggest that silver metallization does not diffuse into the V2O5-doped M-phase ceramics at 900oC, making these materials potential candidates for low-temperature cofired ceramic (LTCC) applications

Predicting morphotropic phase boundary locations and transition temperatures in Pb- and Bi-based perovskite solid solutions from crystal chemical data and first-principles calculations

Using data obtained from first-principles calculations, we show that the position of the morphotropic phase boundary (MPB) and transition temperature at MPB in ferroelectric perovskite solutions can be predicted with quantitative accuracy from the properties of the constituent cations. We find that the mole fraction of PbTiO$_3$ at MPB in Pb(B$'$B$''$)O$_3$-PbTiO$_3$, BiBO$_3$-PbTiO$_3$ and Bi(B$'$B$''$)O$_3$-PbTiO$_3$ exhibits a linear dependence on the ionic size (tolerance factor) and the ionic displacements of the B-cations as found by density functional theory calculations. This dependence is due to competition between the local repulsion and A-cation displacement alignment interactions. Inclusion of first-principles displacement data also allows accurate prediction of transiton temperatures at the MPB. The obtained structure-property correlations are used to predict morphotropic phase boundaries and transition temperatures in as yet unsynthesized solid solutions.Comment: Accepted for publication in J. Appl. Phy

Dynamical trapping and chaotic scattering of the harmonically driven barrier

A detailed analysis of the classical nonlinear dynamics of a single driven square potential barrier with harmonically oscillating position is performed. The system exhibits dynamical trapping which is associated with the existence of a stable island in phase space. Due to the unstable periodic orbits of the KAM-structure, the driven barrier is a chaotic scatterer and shows stickiness of scattering trajectories in the vicinity of the stable island. The transmission function of a suitably prepared ensemble yields results which are very similar to tunneling resonances in the quantum mechanical regime. However, the origin of these resonances is different in the classical regime.Comment: 14 page

Dynamics of open quantum systems initially entangled with environment: Beyond the Kraus representation

We present a general analysis of the role of initial correlations between the open system and an environment on quantum dynamics of the open system.Comment: 5 revtex pages, no figures, accepted for publication in Phys. Rev.