Alumina/yttrium-aluminum garnet crystallographic orientation relationships and interphase boundaries: Observations and interpretation by geometric criteria

ABSTRACTGeometric criteria for low interface energy and interface structure were tested for the cubic-rhombohedral system YAG/alumina. Orientation relationships near (111){110}a // (112){110}y and facets on (111)a(112)y were observed in both sol-gel derived composites and directionally solidified eutectic composites. The ΣYAG=12 near-CSL of 2{111}, {110}, {112} was inferred to be the preferred structural unit. Dislocations with b=1/3{111}a and b=1/2{110}a were observed and inferred to accomodate deviation from the structural unit, respectively. The {110}a,y direction met some of the criteria for an invariant line. Although the OR was explained by geometric criteria it would have been difficult to predict it with such criteria

Download Full-text

Orientation Relationships and Interfaces Between Low Symmetry Phases in The Yttria-Alumina System

MRS Proceedings ◽

10.1557/proc-357-145 ◽

1994 ◽

Vol 357 ◽

Cited By ~ 3

Author(s):

R. S. Hay

Keyword(s):

Monoclinic Phase ◽

Three Dimensional ◽

Real Space ◽

Reciprocal Space ◽

High Symmetry ◽

Orientation Relationships ◽

Yttrium Aluminum ◽

High Resolution Tem ◽

Interphase Boundaries ◽

Definition Of

AbstractInterphase boundaries and orientation relationships for yttria - yttrium-aluminum monoclinic and yttrium-aluminum monoclinic - yttrium-aluminum perovskite eutectics were observed by standard and high resolution TEM techniques. Three and five orientation relationships were found for each system, respectively. These eutectics all had a monoclinic phase and therefore had little potential for high symmetry overlap. In many cases low index planes with similer spacings or spacing multiples were parallel. However, presence of a monoclinic phase made definition of a three-dimensional low index near-CSL very difficult, so a combination of planes corresponding to reciprocal-space directions and zones corresponding to real-space directions were often needed for a geometric description of the orientation relationship. In general, two planes and the real-space direction corresponding to the zone for these planes described the orientation relationships. The disregistry between reciprocal-space coincidence sites was not localized by dislocations large enough to be visible.

Download Full-text

Yag Single Crystals for Scintillators of Stem

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100179580 ◽

1990 ◽

Vol 48 (1) ◽

pp. 166-167

Author(s):

M. Hibino ◽

K. Irie ◽

R. Autrata ◽

P. schauer

Keyword(s):

Single Crystals ◽

Yttrium Aluminum Garnet ◽

Light Guide ◽

Detection System ◽

Polished Surface ◽

Detective Quantum Efficiency ◽

Backscattered Electrons ◽

Electron Detection ◽

Yttrium Aluminum ◽

Phosphor Screens

Although powdered phosphor screens are usually used for scintillators of STEM, it has been found that the phosphor screen of appropriate thickness should be used depending on the accelerating voltage, in order to keep high detective quantum efficiency. 1 It has been also found that the variation in sensitivity, due to granularity of phosphor screens, makes the measurement of fine electron probe difficult and that the sensitivity reduces with electron irradiation specially at high voltages.In order to find out a preferable scintillator for STEM, single crystals of YAG (yttrium aluminum garnet), which are used for detecting secondary and backscattered electrons in SEM were investigated and compared with powdered phosphor screens, at the accelerating voltages of 100kV and 1 MV. A conventional electron detection system, consisting of scintillator, light guide and PMT (Hamamatsu Photonics R268) was used for measurements. Scintillators used are YAG single crystals of 1.0 to 3.2mm thicknesses (with surfaces matted for good interface to the light guide) and of 0.8mm thickness (with polished surface), and powdered P-46 phosphor screens of 0.07mm and 1.0mm thicknesses for 100kV and 1MV, respectively. Surfaces on electron-incidence side of all scintillators are coated with reflecting layers.

Download Full-text