A nanometre‐scale non‐periodic structural variation in high temperature superconducting ceramics and the implications for properties

Abstract

SummaryNon-periodic structural variation has been found in the high T c cuprates, YBa 2 Cu 3 O 7-x and Hg 0.67 Pb 0.33 Ba 2 Ca 2 Cu 3 O 81d , by image analysis of high resolution transmission electron microscope (HRTEM) images. We use two methods for analysis of the HRTEM images. The first method is a means for measuring the bending of lattice fringes at twin planes. The second method is a low-pass filter technique which enhances information contained by diffuse-scattered electrons and reveals what appears to be an interference effect between domains of differing lattice parameter in the top and bottom of the thin foil. We believe that these methods of image analysis could be usefully applied to the many thousands of HRTEM images that have been collected by other workers in the high temperature superconductor field. This work provides direct structural evidence for phase separation in high T c cuprates, and gives support to recent stripes models that have been proposed to explain various angle resolved photoelectron spectroscopy and nuclear magnetic resonance data. We believe that the structural variation is a response to an opening of an electronic solubility gap where holes are not uniformly distributed in the material but are confined to metallic stripes. Optimum doping may occur as a consequence of the diffuse boundaries between stripes which arise from spinodal decomposition. Theoretical ideas about the high T c cuprates which treat the cuprates as homogeneous may need to be modified in order to take account of this type of structural variation.

Cation nonstoichiometry and its contribution to the nanostructured inhomogeneity of tetra and ortho modifications of YBa2Cu3O7 − δ oxide

“…These images confirmed the conclu sions of earlier studies [1,2] on the presence of nano structured inhomogeneity (NSI) in the YBCO super conductor. Having observed deviation of the YBCO cation composition from the stoichiometric Y : Ba : Cu = 1 : 2 : 3 ratio, we argue that the NSI is caused not by variation in the local oxygen content, but by variation in the cation composition due to the presence of coherently embedded nanocrystallites with different cation compositions.…”

“…Only a few papers on studying the nanometer inhomogeneity of the YBCO supercon ductor have been published to date, due to the cleav age of YBCO crystals producing not atomically flat but rough stepped surfaces, making it difficult to identify nanoinhomogeneity against a background of overlap ping contrast. The authors of [1,2] analyzed the con trast in high resolution electron microscope images and the diffuse scattering in electron diffraction pat terns. It was concluded that local nonperiodic distur bances responsible for partitioning the CuO 2 planes into cells with sizes smaller than 0.5 nm along the 〈904〉 directions and 1-2 nm [1] or 5 nm [2] along the 〈110〉 directions were present in the YBCO structure.…”

“…The authors of [1,2] analyzed the con trast in high resolution electron microscope images and the diffuse scattering in electron diffraction pat terns. It was concluded that local nonperiodic distur bances responsible for partitioning the CuO 2 planes into cells with sizes smaller than 0.5 nm along the 〈904〉 directions and 1-2 nm [1] or 5 nm [2] along the 〈110〉 directions were present in the YBCO structure. The authors hypothesized that these structural dis turbances stem from oxygen inhomogeneity.…”

Structural inhomogeneity and twinning inYBa2Cu3O7−δsuperconductors: High-resolution transmission electron microscopy me

“…Structural inhomogeneities were also observed by electron microscopy. [25][26][27][28][29][30][31][32][33] While some of these electron-microscopy studies reported nanosized compositional domains, 25,26,28,29 others reported structural variations at the scale of the twin domain structure, ubiquitous in YBCO, and attributed these variations to inhomogeneities in the O concentration of the twin domains. 30,31,34 Electron-diffraction experiments also revealed local structural inhomogeneities.…”

Aplicação de programa de análise de imagens na interpretação de fotomicrografias de alta resolução de argilominerais

“…A aplicação de análise de imagens em microscopia eletrônica de alta resolução tem sido bastante aplicada em várias áreas das ciências. Como exemplo podem ser citados os estudos, de nanocristais em materiais amorfos, ou parcialmente orientados [2], em fuligem e negro de fumo [3], de estruturas de cerâmicas supercondutoras [4], dentre outros. O presente trabalho aplica um programa de análise de imagens em fotomicrografias de argilas que constituem a fração mais fina dos solos.…”