Synthesis and Microwave Dielectric Properties of SrLa4−x Pr x Ti5O17 (0 ≤ x ≤ 4) Ceramics

Single-phase ceramics in the SrLa_4?x Pr _x La₄Ti₅O₁₇ (0 ≤ x ≤ 4) series were processed via a solid-state sintering route. X-ray diffraction analysis revealed single-phase ceramics for all the compositions. The molar volume (V _m) decreased while the theoretical density (ρ _th) increased with increase in the Pr content. Substitution of Pr³⁺ decreased the relative permittivity (ε _r) and temperature coefficient of resonant frequency (τ _f) due to its smaller ionic polarizability (α _d) and ionic radius than La³⁺. In the present study, ε _r ≈ 54.2, Q _u f ₀  ≈ 7935 GHz, and τ _f  ≈ ?20.3 ppm/°C were achieved for the composition with x = 2 (i.e., SrLa₂Pr₂Ti₅O₁₇).     

Structure and optical properties of heterostructures based on MOCVD (Al x Ga1 − x As1 − y P y )1 − z Si z alloys

Epitaxial heterostructures produced by MOCVD on the basis of Al _x Ga_{1 ? x} As ternary alloys with the composition parameter x ≈ 0.20–0.50 and doped to a high Si and P atomic content are studied. Using the high-resolution X-ray diffraction technique, scanning electron microscopy, X-ray microanalysis, Raman spectroscopy, and photoluminescence spectroscopy, it is shown that the epitaxial films grown by MOCVD are formed of five-component (Al _x Ga_{1 ? x} As_{1 ? y} P _y )_{1 ? z} Si _z alloys.     

Superconducting and structural characteristics of YBa2Cu3O7−x thin films on si(001) substrates with YSZ buffer layers

We have prepared high quality c-axis oriented superconducting YBa₂Cu₃O_7−x thin films on Si(001) substrates covered with YSZ = (ZrO₂ + 10 at.% Y₂O₃) layers by an in situ high pressure (3–5 mbar) oxygen d.c./r.f. sputtering process at substrate temperatures of about 750°C. The films were characterized by X-ray diffraction, transmission electron microscopy (TEM) and electron scanning (SEM) techniques. A superconducting transition temperature T_c(R− 0) = 89 K was determined by resistivity and susceptibility measurements. Cross sectional TEM analysis showed a sharp interface between YSZ and Si; however an inter diffusion zone was observed between YSZ and YBa₂Cu₃O_7−x layers.     

Surface morphology of [11(-2)0] α-plane GaN growth by MOCVD on [1(-1)20]γ-plane sapphire

Nonpolar α-plane[11(-2)0]GaN has been grown on γ-plane[1(-1)02]sapphire by MOCVD,and investigated by high resolution X-ray diffraction and atomic force microscopy.As opposed to the c-direction,this particular orientation is non-polar,and it avoids polarization charge,the associated screenin~charge and the consequent band bending.Both low-temperature GaN buffer and high-temperature/A1N buffer are used for α-plane GaN growth on γ-plane sapphire,and the triangular pits and pleat morphology come forth with different buffers,the possible reasons for which are discussed.The triangular and pleat direction are also investigated.A novel modulate buffer is used for α-plane GaN growth on γ-plane sapphire,and with this technique,the crystal quality has been greatly improved.     

The Thermoelectric Power of Bi1 –xSbx Films (0 ≤ x ≤ 0.15) on Mica and Polyimide Substrates in the Temperature Range of 77–300 K

Semiconductors - The results of an investigation into the thermoelectric power of thin block Bi1 –xSbx films (0 ≤ x ≤ 0.15) 100–1000 nm in thickness on mica and polyimide...