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We have studied the propagation of hard x rays in a planar x-ray waveguide with a sub-20 nm guiding layer. To optimize the transmission and to minimize absorption losses, a novel waveguide design based on a two-component cladding was implemented. Optimized transmission is achieved by placing an appropriate interlayer between the cladding and the guiding core. The experimental results along with simulations of field propagation show that high transmission values can be obtained in waveguide optics at parameters relevant for x-ray imaging. These are small beam diameters below 20 nm and the relatively long guiding length necessary for efficient blocking of multi-keV photon energy beams.

Measurements of lattice parameters and structural refinement were made for a LaGaO 3 , PrGaO 3 , NdGaO 3 , La 0.34 Pr 0.33 Nd 0.33 GaO 3 , and La 0.63 Nd 0.37 GaO 3 samples by powder-diffraction method using synchrotron radiation. The final structure refinement was performed in space group Pbnm at 12 K and room temperature. Anisotropic negative thermal expansion for PrGaO 3 samples was detected. Some anomalies of NdGaO 3 thermal behavior of lattice parameters were observed. The thermal dependence of the Raman spectra of NdGaO 3 single crystals at low temperatures was investigated. Strong interaction of the A g phonon and the crystal-field excitation of the Nd 3ϩ 4 f electrons of the same symmetry was observed. This leads to a renormalization of the wave function and the energy of the phonon and the crystal-field excitation.

The lattice parameter and thermal expansion coefficient ͑TEC͒ for the spinel-type Si 3 N 4 phase prepared under high-pressure and high-temperature conditions are determined for 14 KϽTϽ302 K by x-ray diffraction, at a synchrotron-radiation source, and for 0 KϽTϽ1683 K by first-principles calculations. The low-and high-temperature experimental TEC data are in excellent agreement with the calculations. Our results provide the first experimental evidence that the linear expansion coefficient tends to vanish for TϽ100 K. The experimental temperature dependence of the TEC is accurately represented by polynomials over the complete T range.