Determination of Complex Structures from Powder Diffraction Data: The Crystal Structure of La3Ti5Al15O37

Morris, Russell E.; Owen, Jonathan J.; Stalick, Judith K.; Cheetham, Anthony K.

doi:10.1006/jssc.1994.1198

Cited by 40 publications

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“…LaTi 2 Al 9 O 19 and La 3 Ti 5 Al 15 O 37 ceramics were synthesized through chemical route and characterized using neutron, synchrotron and X-ray diffraction (XRD) techniques [7][8][9]. Morgan prepared LaTi 2 Al 9 O 19 compound through chemical route for better compositional homogeneity [7].…”

Section: Introductionmentioning

confidence: 99%

Dielectric resonators with complex crystal structures in the La2O3–Al2O3–TiO2 system for microwave applications

Dhanya

Unnimaya

Ratheesh

2014

J Mater Sci: Mater Electron

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LaTi 2 Al 9 O 19 and La 3 Ti 5 Al 15 O 37 ceramics in the La 2 O 3 -Al 2 O 3 -TiO 2 system have been prepared by conventional solid state ceramic route. The structure and microstructure of the compositions have been studied using powder X-ray diffraction and scanning electron microscopic techniques. Laser Raman studies have been employed to understand the complex crystal structure of these compositions in molecular level. The microwave dielectric properties of the sintered ceramic compacts were measured by Hakki and Colemann post resonator and TE 01d cavity techniques using a vector network analyzer. LaTi 2 Al 9 O 19 and La 3 Ti 5 Al 15 O 37 ceramics possess excellent microwave dielectric properties such as relatively high unloaded quality factors 7,762 and 7,415, low dielectric constant 15.7 and 22.1 and low temperature coefficient of resonant frequency values -22 and ?18.9 ppm/°C, respectively.

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Section: Introductionmentioning

confidence: 99%

Dielectric resonators with complex crystal structures in the La2O3–Al2O3–TiO2 system for microwave applications

Dhanya

Unnimaya

Ratheesh

2014

J Mater Sci: Mater Electron

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“…7471 A Ê 3 for [(CH 3 ) 4 N] 4 Ge 4 S 10 (Pivan et al, 1994)}, the number of atoms in the asymmetric unit is frequently used as a complexity indicator. Representative examples include structures with 29 atoms in the asymmetric unit, such as gallium phosphite Ga 2 (HPO 3 ) 3 Á 4H 2 O, space group P2 1 (Morris et al, 1992), barium aluminium¯uoride -Ba 3 AlF 9 , space group Pnc2 (Le Bail, 1993), bismuth tri¯uoromethanesulfonate Bi(H 2 O) 4 (OSO 2 CF 3 ) 3 , space group P2 1 ac (Loue È r et al, 1997), and also the structures of uranyl phosphonate (UO 2 ) 3 (HO 3 PC 6 H 5 ) 2 Á H 2 O, space group P2 1 2 1 2 1 , with 50 non-H atoms in the asymmetric unit (Poojary et al, 1996) and La 3 Ti 5 Al 15 O 37 , space group Cc, with 60 atoms in the asymmetric unit (Morris et al, 1994). The most general strategy in structure analysis from high-quality powder diffraction data involves the following stages: (i) the determination of unit-cell constants from indexing methods and derivation of space groups; (ii) the extraction of the integrated intensities, which are converted to structurefactor magnitudes for use in (iii) methods of solving the phase problem; (iv) the re®nement of the approximate structure model with the Rietveld method.…”

Section: Methodology For Structure Solution From Powder Datamentioning

confidence: 99%

Advances in Powder Diffraction Analysis

Louër¹

1998

Acta Cryst Sect A

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Powder diffraction offers a wide spectrum of applications to solid-state scientists. The method traditionally used for phase analysis and the study of structural imperfections has bene®ted, in the last twenty years, from great advances in the instrumentation and computer-based approaches for pattern indexing and modelling. The factors at the origin of the metamorphosis of the method are presented. The major modern applications reported include quantitative analysis and the extraction of three-dimensional structural and microstructural properties. The use of pattern-®tting techniques for the characterization of the microstructure is discussed through applications to nanocrystalline materials. Remarkable results achieved in the solution of crystal structures are presented, as well as the impact in solid-state chemistry of powder crystallography, particularly for elucidating the crystal chemistry of families of compounds for which only powders are available. New strategies for solving the phase problem have been introduced and new classes of solids are being studied, such as drugs, coordination and organic compounds.

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“…The situation has largely improved in the last two years. The structure of La3TisAllsO37, which has 60 atoms in the asymmetric unit (space group Cc), is the largest structure ever solved from powder data (Morris, Owen, Stalick & Cheetham, 1994). Direct methods localized a limited number of atoms: the structure could be completed by exploiting the supplemental information contained in a neutron powder pattern and structure refinement was accomplished by using suitable geometric restraints in the least-squares process.…”

Section: About the Size Of The Structures Solvable By Direct Methodsmentioning

confidence: 99%

Direct Methods and Powder Data: State of the Art and Perspectives

Giacovazzo¹

1996

Acta Cryst Sect A

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Solving crystal structures by applying direct methods to single-crystal data is a relatively easy task for structures with up to 100 atoms in the asymmetric unit. Their successful application to powder data is still a challenge unless the size of the structure is moderate. The rate of success depends on several factors like the efficiency of the full-pattern-decomposition programs, the peak overlapping, the presence of preferred orientation in the powder specimen, the nature of the background, the type of radiation used for collecting experimental data etc. The main factors are analysed in order to provide a clear description of the specific problems that have to be forced when direct phasing from powder data is attempted.

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Determination of Complex Structures from Powder Diffraction Data: The Crystal Structure of La3Ti5Al15O37

Cited by 40 publications

References 0 publications

Dielectric resonators with complex crystal structures in the La2O3–Al2O3–TiO2 system for microwave applications

Dielectric resonators with complex crystal structures in the La2O3–Al2O3–TiO2 system for microwave applications

Advances in Powder Diffraction Analysis

Direct Methods and Powder Data: State of the Art and Perspectives

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