The preparation, modeled and refined crystal structures, and structure−dielectric property relationships of five Ba3MM‘2O9 (M = Mg, Ni, Zn; M‘ = Nb, Ta) perovskites are reported. Crystal structure modeling was used to generate initial structure models for Rietveld refinements of the neutron powder diffraction data. Bond valence sums calculated from the bond distances indicate Ba−O bonds are compressed and the M−O and M‘−O6 bonds are expanded from ideal lengths. A shift of Ta5+ and Nb5+ out of center of the [M‘O6] octahedra forms three short and three long M‘−O bonds. The octahedral distortion is driven by the asymmetry in the O bonding network and aided by the second-order Jahn−Teller distortion of the d0 Nb5+ and Ta5+ cations. Differences in the atomic coordination environments in the crystal structures were utilized to propose crystal structure−dielectric property relationships. The coordination of the divalent B-site cation (M2+) was correlated with the temperature coefficient of the resonant frequency...

Crystal Structures, Modeling, and Dielectric Property Relationships of 2:1 Ordered Ba3MM'2O9 (M ) Mg, Ni, Zn; M' ) Nb, Ta) Perovskites

The effect of a slight A- and B-site cation nonstoichiometry on the structure, densification, and microwave dielectric properties of Ba(Mg1/ 3Ta2/3)O3 (BMT) was investigated. Magnesium and barium nonstoichiometric compositions based on Ba(Mg0.33-xTa0.67)O3 [x = −0.015, −0.010, −0.005, 0.0, 0.005, 0.010, 0.015, 0.020, 0.025, and 0.030] and Ba1-x(Mg0.33Ta0.67)O3 [x = −0.015, −0.010, −0.005, 0.0, 0.0025, 0.005, 0.0075, 0.010, 0.015, 0.020, 0.025, and 0.030] were prepared using the conventional solid-state ceramic route. The lattice distortion and cation ordering were determined using X-ray diffraction technique. The phase composition and surface morphology were studied by EDX and scanning electron microscopy techniques, respectively. The sintered samples were characterized in the microwave frequency range using the resonance technique. It is found that a slight barium or magnesium deficiency can improve density, microwave dielectric properties, and cation ordering, while the addition of excess ions deteriora...

Effect of Nonstoichiometry on the Structure and Microwave Dielectric Properties of Ba(Mg0.33Ta0.67)O3

The effect of glass additives on the microwave dielectric properties of Ba(Mg1/3Ta2/3)O3 ceramics

The samples of complex perovskite Ba(Mg1/3Ta2/3)O3 (BMT) were synthesized at various sintering temperatures and the X-ray diffraction (XRD) patterns and Raman spectra of the samples were collected. Both the structure refinements using the XRD data and the Raman spectra show that the samples sintered above 1500°C with high pellet relative density (>95%) take almost-perfect B-site-ordered structure; while the samples sintered below 1400°C with low pellet relative density (<70%) take the more disordered structure at B-sites. The vibrational modes of 1:2 ordered BMTwere obtained and illustrated by using first-principle calculations. With the assistance of the calculation results, Raman peaks of BMT were assigned as A1g(1) (107 cm−1), A1g(2) (212 cm−1), A1g(3) (433 cm−1), A1g(4) (798 cm−1), and Eg(1) (104 cm−1), Eg(2) (160 cm−1), Eg(3) (264 cm−1), Eg(4) (386 cm−1), Eg(5) (576 cm−1). The highly ordered BMT sample at B-site shows longer phonon lifetime and weaker coupling among phonons than the disordered BMT, which probably are the intrinsic reasons for the highly ordered BMT sample to have the low dielectric loss.

XRD and Raman Studies on the Ordering/Disordering of Ba(Mg1/3Ta2/3)O3

In recent years, research in organophosphorus chemistry has mainly focused in designing newer and better phosphorus ligands for synthesizing novel metal complexes with improved catalytic activities. Aminophosphines [tricoordinate phosphorus(III)–nitrogen systems] are considered as versatile compounds owing to the presence of nitrogen centres which, in principle, can influence additional reactivity features. They are quite sensitive to air and moisture due to the presence of polar PN bond(s). In spite of this, research in aminophosphine chemistry is gaining momentum day-by-day and this is due mainly to one reason: their rich behaviour as ligands in metal complex chemistry and subsequently in catalysis. Their role as synthons in inorganic heterocyclic chemistry has also helped produce new types of heterocycles. In this paper, the chemistry of simple acyclic aminophosphines (synthesis, characterization, reactivity and applications) is covered and particular focus is given to their ability to form chalcogenides along with their role played as ligands in coordination chemistry and as synthons in inorganic heterocyclic chemistry. Copyright © 2009 John Wiley & Sons, Ltd.

Aminophosphines: their chemistry and role as ligands and synthons

Structural analysis of BaMg1/3(Ta,Nb)2/3O3 ceramics

Structure analysis on the Ba3Mg(Ta1−xNbx)2O9 ceramics: Coexistence of order and disorder

The title compound (C6H5)2(OC4H8N)P=N−S3N3 crystallizes in the space group\(P\bar 1\) with unit cell parametersa=9.3900(2),b=9.4747(1),c=11.3850(3) A, α=95.73(4), β=96.85(6), γ=104.26(2)o, and Z=2. The tricoordinated sulfur of the cyclotrithiazene ring deviates from the mean plane of other skeletal atoms by 0.683(4) A. The angle at this atom is the smallest in the ring and is enclosed by the longest S−N bonds observed in the ring.

Crystal structure of (diphenyl)(morpholino)phosphiniminocyclotrithiazene

A new phase of Ba(Mg1/3Ta2/3)O3 has been obtained by calcination at 1400°C. It belongs to the cubicPm3m witha = 4·08840(4)A and the crystal structure has been found to be the ideal perovskite by the Rietveld method from powder X-ray diffraction data.

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Crystal structure of Ba(Mg1/3Ta2/3)O3 calcinated at 1400°C

The title compound (OC4H8N)3P=N–S3N3 crystallizes in a monoclinic crystal system with unit cell parameters a = 89996(3), b = 172895(7), and c = 123648(9) A, β = 9063(5)°, Z = 4, and space group P21/n Strikingly the exocylic S1–N4 bond length is 1545(3) AR and is accompanied by the largest angle at P–N4–S1 as 1312(2)° The tricoordinated sulfur atom of the cyclotrithiazene ring deviates from the mean plane of other five atoms by 0654(1) A

G. Sreenivasa Murthy

Papers

Structural analysis of BaMg1/3(Ta,Nb)2/3O3 ceramics

Structure analysis on the Ba3Mg(Ta1−xNbx)2O9 ceramics: Coexistence of order and disorder

Crystal structure of (diphenyl)(morpholino)phosphiniminocyclotrithiazene

Crystal structure of Ba(Mg1/3Ta2/3)O3 calcinated at 1400°C

Crystal structure of trismorpholino phosphiniminocyclotrithiazene