ABSTRACT
Correlating electromechanical and dielectric properties with nanometre-scale order is the defining challenge for the development of piezoelectric oxides. Current lead (Pb)-based relaxor ferroelectrics can serve as model systems with which to unravel these correlations, but the nature of the local order and its relation to material properties remains controversial. Here we employ recent advances in diffuse scattering instrumentation to investigate crystals that span the phase diagram of PbMg1/3Nb2/3O3-xPbTiO3 (PMN-xPT) and identify four forms of local order. From the compositional dependence, we resolve the coupling of each form to the dielectric and electromechanical properties observed. We show that relaxor behaviour does not correlate simply with ferroic diffuse scattering; instead, it results from a competition between local antiferroelectric correlations, seeded by chemical short-range order, and local ferroic order. The ferroic diffuse scattering is strongest where piezoelectricity is maximal and displays previously unrecognized modulations caused by anion displacements. Our observations provide new guidelines for evaluating displacive models and hence the piezoelectric properties of environmentally friendly next-generation materials.
ABSTRACT
Quantitative analytical methods have been defined for the determination of cefpimizole, a new broad-spectrum cephalosporin antibiotic, in plasma and urine specimens. The methods employ ion-pair reversed-phase high-performance liquid chromatography with both ethylene-diaminetetraacetic acid (EDTA) and tetrabutylammonium hydroxide as pairing agents for separation and ultraviolet detection at 254 nm. Sample preparation for plasma aliquots consisted of acetonitrile protein precipitation followed by phase separation; the aqueous phase was filtered and assayed. For urine, sample preparation consisted of diluting an aliquot with chromatographic eluent, filtering, and assaying. The methods had a linear range of 17-0.3 micrograms/ml for plasma and 800-15 micrograms/ml for urine and had sufficient precision and accuracy to provide quantitative data. Stability studies in plasma and urine indicated that cefpimizole degraded rapidly at room temperature. Addition of EDTA to the physiological fluid substantially increased the stability at room temperature, and little or no degradation was observed in plasma or urine stored at -30 degrees C for over 100 days. Utility of the methods was demonstrated by assaying plasma and urine specimens obtained from a human volunteer receiving three dose levels. Estimates of various pharmacokinetic parameters are presented.