Transmission electron microscopy was used to study the ordered domain structures in undoped and La/Na-doped Pb(Mg,/,NbZ/,)03 (PMN), where the compositions of the doped samples were specifically chosen so as to elucidate the ordering mechanism. The results showed that the Mg2+ ions and Nb5+ ions are short-range ordered on the B-site sublattice in undoped PMN, with a domain sue of 2 to 5 nm. This short-range ordering gives rise to B-site composition fluctuations occurring on a nanometer scale, and it is this compositional inhomogeneity which is believed to be responsible for the diffuse phase transition behavior. Donor doping with La203 can compensate for the I d charge imbalance resulting from the short-range order and thus enhances the degree of ordering. Acceptor doping with NaZO, however, increases the charge effect, and hence ordering is suppressed. The effect of Na doping and La doping on the dielectric properties of PMN is also discussed. [

The fracture behavior of Al,O, containing 5 vol% 0.15 pm SIC particles was investigated using indentation techniques. A significant increase in strength was achieved by the addition of SIC particles to the base AI,O,. Specifically, the strength increased from 560 MPa for A1,0, to 760 MPa for the composite samples (average values for unindented hotpressed bars tested in four-point bending). After annealing for 2 h at 1300°C, the average strength of the composite samples increased to about 1000 MPa. Toughness was estimated using indentation-strength data. While there was a slight increase in toughness, the increase was not sufficient to account for the increase in the unindented strength on Sic particle addition. It is suggested that the observed strengthening and apparent toughening were due to a machining-induced compressive surface stress.

The framed standard model (FSM) is obtained from the standard model by incorporating, as field variables, the frame vectors (vielbeins) in internal symmetry space. It gives the standard Higgs boson and 3 generations of quarks and leptons as immediate consequences. It gives moreover a fermion mass matrix of the form: m = m T αα † , where α is a vector in generation space independent of the fermion species and rotating with changing scale, which has already been shown to lead, generically, to up-down mixing, neutrino oscillations and mass hierarchy. In this paper, pushing the FSM further, one first derives to 1-loop order the RGE for the rotation of α, and then applies it to fit mass and mixing data as a first test of the model. With 7 real adjustable parameters, 18 measured quantities are fitted, most (12) to within experimental error or to better than 0.5 percent, and the rest (6) not far off. (A summary of this fit can be found in Table 2 in the text.) Two notable features, both generic to FSM, not just specific to the fit, are: (i) that a theta-angle of order unity in the instanton term 1 in QCD would translate via rotation into a Kobayashi-Maskawa phase in the CKM matrix of about the observed magnitude (J ∼ 10 −5 ), (ii) that it would come out correctly that m u < m d , despite the fact that m t m b , m c m s . Of the 18 quantities fitted, 12 are deemed independent in the usual formulation of the standard model. In fact, the fit gives a total of 17 independent parameters of the standard model, but 5 of these have not been measured by experiment. 2 while su(2) is already known to represent up-down flavour [6] andũ(1) is B − L [7].

The tensile creep behavior of two ceramic composite systems exhibiting duplex microstructures was studied relative to their single-phase constituents in the temperature and stress ranges of 1100-1350°C and 35-75 MPa. The equivolumetric compositions in the Al,O,:c-ZrO, (8 mol% Y,O,) and AI,O,:Y,AI,O,, systems both exhibit lower creep rates than either of their single-phase constituents. This effect is attributed to Y3+ (and possibly Zr4+) present in the AI,O, as a segregant which lowers the creep rate by -2 orders of magnitude. It is believed that the segregation of Y3+ to the AI,O, grain boundaries hinders the interface reaction believed to control the creep. If one of the singlephase constituents is taken to be the Y3+-doped A1,0,, the creep of the duplex microstructures can be modeled using standard composite theory applied to flow.

Nb-doped BaTi03 has been prepared with various Ba/(Ti +Nb) ratios such that single-phase products will be obtained if the charged donor center is assumed to be compensated in turn by Ba vacancies, Ti vacancies, equal concentrations of the two cation vacancies, oxygen interstitials, or electrons. For air-fired samples, examination by transmission electron microscopy showed that only the composition adjusted for compensation by titanium vacancies was single phase. The other compositions contained a Ti-rich second phase in order to achieve a matrix with the appropriate concentration of titanium vacancies. When sintered in a reducing atmosphere, compensation was by electrons, and a Ba-rich second phase was present in the composition adjusted to give compensation by titanium vacancies, The results indicate that for donor concentrations greater than ~0 . 5 mol% in BaTiO,, charge compensation is achieved by Ti vacancies under oxidizing conditions, and by electrons (as is well-known) under reducing conditions. The effect of compensating defects on grain growth is also discussed.

This paper describes the results of detailed studies carried out on Ca‐doped and Nb‐doped BaTiO3 using scanning electron microscopy and transmission electron microscopy. The techniques used were topographical contrast, selected‐area diffraction, and microdiffraction Kikuchi pattern analysis. By these methods it was possible to unambiguously identify the different types of domain boundaries. Also, evidence was obtained for the existence of an unconventional 90% domain boundary which has not previously been reported.

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A number of preliminary observations have guided this The tensile creep behavior of two rare-earth dopant sysstudy. For example, it is known that the bulk solubility of Y 3ϩ tems, lanthanum-and yttrium-doped alumina, are comand La 3ϩ in alumina is very small 11,12 and the size mismatch pared and contrasted in order to better understand the role between Al 3ϩ and the aforementioned dopant cations is quite of oversized, isovalent cation dopants in determining creep large. Thus, it might be expected that Y and La ions will behavior. It was found that, despite some microstructural segregate preferentially to extended defects, such as free surdifferences, these systems displayed qualitatively a similar faces and grain boundaries. This expectation was validated in a improvement in creep resistance, supporting the hypothesis previous SIMS (secondary ion mass spectroscopy) mapping that creep is strongly influenced by segregation. Differences study 13 and STEM (scanning transmission electron microscopy) in primary creep behavior and activation energy for steadywork 14,15 in which both Y and La dopant segregation was state creep were, however, observed for these systems. Given observed. Indeed, sintering studies show that Y and La retard these results, it is expected that creep behavior can be furgrain growth and greatly reduce the densification rate in these ther optimized by adjusting the dopant level and by controlsystems. 16 Further, it has been reported that Y can reduce the ling the microstructure.growth of polycrystalline alumina scales. 17 As mentioned above, the present work consists of tensile I. Introduction creep testing and microstructural characterization of both Yand La-doped alumina. Microstructural analyses center on M ECHANICAL properties of structural ceramics in a highquantifying differences in average grain size and shape between temperature environment have been the subject of numerthese two systems as well as grain evolution during the test. The ous investigations over the years. For this reason, creep goal of this effort is to relate microstructural features of the properties have been studied and modeled extensively, and oxide to the (macroscopic) steady-state creep rate, as detercreep mechanisms are well-established. [1][2][3][4] In particular, much mined by a tensile creep test. As will be seen below, such comrecent work has involved the addition of impurities and the plementary testing is helpful in formulating structure-property tailoring of microstructures with the goal of obtaining desirable relations. properties over a range of temperatures. The creep rate in doped alumina depends strongly on the type of dopant, and most single dopants have been found either to increase the creep rate