Crystal Chemistry of New Calcium Tantalate Dielectric Materials

1998 ◽  
Vol 547 ◽  
Author(s):  
Ian E. Grey ◽  
Robert S. Roth ◽  
Gus Mumme ◽  
Leonid A. Bendersky ◽  
Dennis Minor
Keyword(s):  
Dielectric Materials ◽  
Structure Property ◽  
X Ray ◽  
Structure Property Relationships ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Unit Cells ◽  
Communication Devices ◽  
Fluorite Type ◽  
Diffraction Patterns

AbstractDoping of calcium tantalate, Ca2Ta2O7, with small amounts (<5 mole%) of Ca2Nb2O7 results in a 50% increase in the dielectric constant, K (from 23 to 35 at 1 MHz), and a zero temperature coefficient of K is achieved at about 18 mole% of Ca2Nb2O7. This opens up the possibility of applications in microwave communication devices. Crystallographic information needed to understand the structure/property relationships in this system is lacking. We have prepared samples of calcium tantalates doped with different elements including Nb, Sm, Ti, Nd and Zr, and have structurally characterised them using X-ray diffraction and transmission electron microscopy. The diffraction patterns of the tantalates all display strong subcell reflections characteristic of the trigonal weberite structure together with complex distributions of superlattice reflections that depend on the nature and concentration of the dopant and on the reaction temperature. The diffraction patterns were indexed using related trigonal or pseudo-trigonal unit cells with a ~7.3 Å, c ~ n × 6 Å. Polytypes with n = 3, 4, 5, 6 and 7 were prepared as single crystals by the flux method. Single crystal X-ray data was used in conjunction with high resolution electron microscope images to solve the structures. Details are given for a 6M polytype (M=monoclinic). A characteristic structural feature of the polytypes is a fluorite-type cation array which is periodically twinned on (111)f to give mixed cubic-hexagonal stacking of the cation layers. The structure relations with the pyrochlore and weberite structures are discussed.

Effect of temperature on formation of murataite and murataite-pyrochlore ceramics

2002 ◽  
Vol 757 ◽  
Author(s):  
O. I. Kirjanova ◽  
S. V. Stefanovsky ◽  
S. V. Yudintsev
Keyword(s):  
Effect Of Temperature ◽  
Cold Crucible ◽  
Iron Group ◽  
X Ray Diffraction ◽  
X Ray ◽  
Oxide Solid Solution ◽  
Transmission Electron ◽  
Heat Treated ◽  
Unit Cells ◽  
Fluorite Type

ABSTRACTProcesses of phases formation in the ceramic mixtures with basic compositions (wt.%) 10 CaO, 10 MnO, 5 Al2O3, 5 Fe2O3, 55 TiO2, 5 ZrO2, 10 UO2 (M1) and 8 CaO, 8 MnO, 4 Al2O3, 4 Fe2O3, 20 Gd2O3, 44 TiO2, 4 ZrO2, 8 UO2 (M4) were studied using X-ray diffraction, scanning and transmission electron microscopy. The batches were milled, compacted in pellets at 200 MPa, and heat-treated in a resistive furnace at 1100 °C, 1300 °C, 1400 °C, and 1500 °C as well as melted in a cold crucible at ∼1600 °C. Reactions in the mixtures heat-treated at 1100 °C were not completed and samples contained significant amount of unreacted and intermediate (altered rutile, cubic oxide solid solution, perovskite) phases. Within the temperature range 1100–1300 °C reactions are mainly completed and ceramics sintered at 1300 °C are composed of major murataite and minor rutile (M1) or major murataite and pyrochlore and minor zirconolite and perovskite (M4). However full homogenization at 1300 °C has not been reached yet and to obtain the ceramics with uniform compositions of the phases sintering at 1400 °C or melting at 1500–1600 °C were required.In the ceramic sample M1 two murataite varieties with five- (murataite-5C) and eight-fold (mu-rataite-8C) fluorite-type unit cells were found. The sample M4 is composed of pyrochlore, murataite-8C and zirconolite-3O. In the sample M1 murataite-5C is enriched with U and Ca and depleted with iron group elements as compared to murataite-8C. Fraction of murataite-5C concentrates about 80% of total U and about 70% of Mn+Fe (corrosion products). Waste elements partitioning among the phases in the M4 sample depends significantly on temperature of heat-treatment.

Imaging of crystalline structure in thermotropic copolymers

1990 ◽  
Vol 48 (4) ◽  
pp. 226-227
Author(s):  
Richard J. Spontak ◽  
Alan H. Windle
Keyword(s):  
Diffraction Analysis ◽  
Crystalline Structure ◽  
Dark Field ◽  
Advanced Materials ◽  
Structure Property ◽  
Razor Blade ◽  
Transparent Films ◽  
Structure Property Relationships ◽  
Transmission Electron ◽  
Diffraction Patterns

Electron-diffraction analysis and dark-field (DF) imaging of crystalline structure in highly-oriented polymers have been used effectively to discern structure-property relationships in these materials. Diffraction patterns of some thermotropic copolyesters, such as those composed of 4-hydroxybenzoic acid (B) and 2,6-hydroxynaphthoic acid (N) or those from N and terephthalic acid/hydroxyaniline (TA), exhibit sharp equatorial reflections, suggestive of finite intermolecular ordering, and aperiodic meridional maxima, indicative of random intramolecular sequencing (see inset of Fig. 1). However, diffraction analysis of a related thermotropic copolymer, composed of B and isophthalic acid/hydroquinone (IQ), reveals periodic meridional maxima and ill-defined equatorial reflections. DF imaging in conventional transmission electron microscopy is utilized here to permit accurate assessment of the crystallite morphologies in these two chemically-related families.Samples of the B-N and N-TA materials were provided by the Hoechst-Celanese Corporation, and the B-IQ copolymer was supplied by ICI Advanced Materials. Electron-transparent films were produced by first heating a small chunk of each material on freshly-cleaved rocksalt to a predesignated temperature. The samples were then quickly sheared with a razor blade, and the resultant films were quenched on an aluminum block.

Crystal Structures Of L-Nb205 AND L-Ta205

1977 ◽  
Vol 35 ◽  
pp. 188-189
Author(s):  
Sumio Iijima
Keyword(s):  
Electron Microscope ◽  
Complex Nature ◽  
X Ray Diffraction ◽  
X Ray ◽  
Resolution Electron ◽  
Unit Cells ◽  
System 2 ◽  
High Resolution Electron Microscope ◽  
Diffraction Patterns ◽  
Phase Relationships

Although structures of tantalum pentoxides have been extensively studied, they have not been fully understood because of the complex nature of their X-ray diffraction patterns. In this study we made some observations on crystals of L-Ta2O5 and L-Nb2O5 using a high resolution electron microscope. The latter structure has been believed to be isostructural with L-Ta2O5. The samples were prepared by Dr. Roth at NBS and were parts of the products used for determining phase relationships in niobium pentoxides (1) and the Ta2O5-Ta2WO8 system (2).According to the X-ray data both structures have orthorhombic unit cells with a = 6.2, b = 29.3, c = 3.9Å. The structures are based on the U03-type and the b spacings are nearly 8 times those of the subcell. Electron diffraction (E.D.) patterns of L-Nb2O5 and L-Ta3O5 crystals showing a*-b* reciprocal sections confirmed generally the results of X-ray works (Figs, la and lc).

Atomic Scale Structure-Property Relationships of Defects and Interfaces in Ceramics

1998 ◽  
Vol 4 (S2) ◽  
pp. 556-557
Author(s):  
S. Stemmer ◽  
G. Duscher ◽  
E. M. James ◽  
M. Ceh ◽  
N.D. Browning
Keyword(s):  
Point Defects ◽  
High Resolution Electron Microscopy ◽  
Complete Characterization ◽  
Atomic Scale ◽  
Structure Property ◽  
Defect Engineering ◽  
Impurity Atoms ◽  
Structure Property Relationships ◽  
Resolution Electron ◽  
Scale Composition

The evaluation of the two dimensional projected atom column positions around a defect or an interface in an electronic ceramic, as it has been performed in numerous examples by (quantitative) conventional high-resolution electron microscopy (HRTEM), is often not sufficient to relate the electronic properties of the material to the structure of the defect. Information about point defects (vacancies, impurity atoms), and chemistry or bonding changes associated with the defect or interface is also required. Such complete characterization is a necessity for atomic scale interfacial or defect engineering to be attained.One instructive example where more than an image is required to understand the structure property relationships, is that of grain boundaries in Fe-doped SrTi03. Here, the different formation energies of point defects cause a charged barrier at the boundary, and a compensating space charge region around it. The sign and magnitude of the barrier depend very sensitively on the atomic scale composition and chemistry of the boundary plane.

Cetyltrimethylammonium bromide- and ethylene glycol-assisted preparation of mono-dispersed indium oxide nanoparticles using hydrothermal method

2014 ◽  
Vol 68 (8) ◽  
Author(s):  
Selvakumar Dhanasingh ◽  
Dharmaraj Nallasamy ◽  
Saravanan Padmanapan ◽  
Vinod Padaki
Keyword(s):  
Ethylene Glycol ◽  
Hydrothermal Method ◽  
Indium Oxide ◽  
Cetyltrimethylammonium Bromide ◽  
Oxide Nanoparticles ◽  
X Ray Diffraction ◽  
Hydrothermal Conditions ◽  
X Ray ◽  
Transmission Electron ◽  
Diffraction Patterns

AbstractThe influence of cetyltrimethylammonium bromide and ethylene glycol on the size and dispersion of indium oxide nanoparticles prepared under hydrothermal conditions was investigated. The precursor compound, indium hydroxide, obtained by the hydrothermal method in the absence as well as the presence of cetyltrimethylammonium bromide, was converted to indium oxide by sintering at 400°C. The formation of nanoscale indium oxide upon sintering was ascertained by the characteristic infrared adsorption bands and X-ray diffraction patterns of indium oxide. Transmission electron microscopy and band gap values confirmed that the cetyltrimethylammonium bromide facilitated the formation of indium oxide nanoparticles smaller in size and narrower in distribution than those prepared without the assistance of cetyltrimethylammonium bromide.

Study of naphthopyran derivatives: structure and photochromic properties in solution and in polymer film

2021 ◽  
Vol 77 (7) ◽  
Author(s):  
Linqi Shi ◽  
Zipei Sun ◽  
Jiajie Tian ◽  
Yaodong Huang ◽  
Jiben Meng
Keyword(s):  
Uv Light ◽  
Steric Effects ◽  
Pmma Film ◽  
Structure Property ◽  
Photochromic Properties ◽  
X Ray ◽  
Structure Property Relationships ◽  
Substituent Group ◽  
Uv Light Irradiation ◽  
Electronic And Steric Effects

Four naphthopyran derivatives, namely, 3,3-bis(naphthalen-1-yl)-3H-naphtho[2,1-b]pyran, C33H22O, NP1, 3,3-bis([1,1′-biphenyl]-4-yl)-3H-naphtho[2,1-b]pyran, C37H26O, NP2, 3,3-bis(4-phenoxyphenyl)-3H-naphtho[2,1-b]pyran, C37H26O2, NP3, and 3,3-bis(4-methoxy-2-methylphenyl)-3H-naphtho[2,1-b]pyran, C29H26O3, NP4, were synthesized and their photochromic properties investigated. NP1–NP4 exhibited good photochromism in different solutions and in poly(methyl methacrylate) (PMMA) film under UV light irradiation. Solvatochromism and the electronic and steric effects of the substituent group on photochromism were analyzed and decolouration curves were found to fit a monoexponential kinetic decay in most cases. Single-crystal X-ray analysis of NP1 and NP2 revealed the structure–property relationships. Good fatigue resistance of NP1, both in solution and in the PMMA film, endows it with potential value for applications.

The Defect Fluorite Phase in the ZrO2-PrO1.5 System and Its Relationship to the Structure of Pyrochlore

1992 ◽  
Vol 45 (9) ◽  
pp. 1375 ◽  
Author(s):  
RL Withers ◽  
JG Thompson ◽  
PJ Barlow ◽  
JC Barry
Keyword(s):  
Solid Solution ◽  
Point Defects ◽  
Phase Field ◽  
Fluorite Phase ◽  
X Ray ◽  
Average Structure ◽  
Transmission Electron ◽  
Solution Field ◽  
Close Relationship ◽  
Fluorite Type

A detailed transmission electron microscope and X-ray powder diffraction study has been made of the so-called 'defect fluorite' phase field in the ZrO2-PrO1.5 system and of its close relationship to the pyrochlore solid solution field in the same system. Even for the lowest possible PrO1.5 content within the 'defect fluorite' phase field, it is clear that the sharp Bragg reflections characteristic of the underlying fluorite average structure are accompanied by some of the 'satellite reflections' characteristic of the pyrochlore solid solution field. As the PrO1.5 content increases, these satellite reflections increase systematically in intensity as well as sharpening very considerably. It is shown that this 'defect fluorite' phase field cannot be adequately described either in terms of random point defects within an average fluorite-type matrix or in terms of a diphasic texture of pyrochlore domains embedded coherently into a fluorite matrix, but must be regarded as enuinely intermediate between these two end-member structures and of commensurately modulated fluorite type. A group theoretical approach is used to propose a model for the structural deviation from the underlying fluorite average structure.

Facile Refluxing Synthesis of Hydroxyapatite Nanoparticles

2015 ◽  
Vol 68 (8) ◽  
pp. 1293 ◽  
Author(s):  
Pakvipar Chaopanich ◽  
Punnama Siriphannon
Keyword(s):  
Crystallite Size ◽  
Reaction Times ◽  
Single Step ◽  
Hydroxyapatite Nanoparticles ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Aqueous Mixture ◽  
Diffraction Patterns ◽  
Microscopy Images

Hydroxyapatite (HAp) nanoparticles were successfully synthesized from an aqueous mixture of Ca(NO3)2·4H2O and (NH4)2HPO4 by a facile single-step refluxing method using polystyrene sulfonate (PSS) as a template. The effects of reaction times, pH, and PSS concentration on the HAp formation were investigated. It was found that the crystalline HAp was obtained under all conditions after refluxing the precursors for 3 and 6 h. The longer refluxing time, the greater the crystallinity and the larger the crystallite size of the HAp nanoparticles. The HAp with poor crystallinity was obtained at pH 8.5; however, the well-crystallized HAp was obtained when reaction pH was increased to 9.5 and 10.5. In addition, the X-ray diffraction patterns revealed that the presence of PSS template caused the reduction of HAp crystallite size along the (002) plane from 52.6 nm of non-template HAp to 43.4 nm and 41.4 nm of HAp with 0.05 and 0.2 wt-% PSS template, respectively. Transmission electron microscopy images of the synthesized HAp revealed the rod-shaped crystals of all samples. The synthesized HAp nanoparticles were modified by l-aspartic acid (Asp) and l-arginine (Arg), having negative and positive charges, respectively. It was found that the zeta potential of HAp was significantly changed from +5.46 to –24.70 mV after modification with Asp, whereas it was +4.72 mV in the Arg-modified HAp. These results suggested that the negatively charged amino acid was preferentially adsorbed onto the synthesized HAp surface.

Structure/Property Relationships of Seashells

2004 ◽  
Vol 844 ◽  
Author(s):  
David J. Scurr ◽  
Stephen J. Eichhorn
Keyword(s):  
Raman Band ◽  
Surface Damage ◽  
Structure Property ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Property Relationships ◽  
Energy Variable ◽  
Insight Into ◽  
Characterisation Techniques ◽  
Scanning Electron

ABSTRACTThis study uses various characterisation techniques on the razor shell (Ensis siliqua), to relate the shell's microstructure to its mechanical properties. Scanning electron microscopy (SEM) has shown that the outer and inner regions of the shell are composed of simple and complex crossed lamellar microstructures respectively. These layers are interspersed by prismatic layers of a completely different crystallographic orientation. Nanoindentation and microhardness measurements have shown that the structure is anisotropic, and Raman band shifts have been observed within these indented/deformed areas of shell, showing that the microstructure deforms rather than generating surface damage. The use of energy variable synchrotron X-ray diffraction has shown that the calcium carbonate crystals of the shell are preferentially orientated as a function of depth and that opposing residual stresses exist at the outer and inner regions of the shell. This study has analysed several microstructural features of the shell and provided an insight into how they prevent failure of the material.

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