We report piezoelectric materials composed of charge-compensated co-doped (Mg, β)(x)Al(1-x)N (β = Zr or Hf) thin films. The effect of the dopant element into AlN on the crystal structure, and piezoelectric properties of co-doped AlN was determined on the basis of a first-principles calculation, and the theoretical piezoelectric properties were confirmed by experimentally depositing thin films of magnesium (Mg) and zirconium (Zr) co-doped AlN (Mg-Zr-doped AlN). The Mg-Zrdoped AlN thin films were prepared on Si (100) substrates by using a triple-radio-frequency magnetron reactive co-sputtering system. The crystal structures and piezoelectric coefficients (d33) were investigated as a function of the concentrations, which were measured by X-ray diffraction and a piezometer. The results show that the d33 of Mg-Zr-doped AlN at total Mg and Zr concentrations (both expressed as β) of 0.35 was 280% larger than that of pure AlN. The experimentally measured parameter of the crystal structure and d33 of Mg-Zr-doped AlN (plotted as functions of total Mg and Zr concentrations) were in very close agreement with the corresponding values obtained by the first-principle calculations. Thin film bulk acoustic wave resonators (FBAR) employing (Mg,Zr)0.13Al0.87N and (Mg, Hf)0.13 Al0.87N as a piezoelectric thin film were fabricated, and their resonant characteristics were evaluated. The measured electromechanical coupling coefficient increased from 7.1% for pure AlN to 8.5% for Mg-Zr-doped AlN and 10.0% for Mg- Hf-doped AlN. These results indicate that co-doped (Mg, β)(x)Al(1-x)N (β = Zr or Hf) films have potential as piezoelectric thin films for wideband RF applications.
Elastic properties of (1-x)(Na 0.5 Bi 0.5 )TiO 3 -xBaTiO 3 0.01, 0.02, 0.03, 0.05, 0.08) are measured by the Brillouin scattering method to clarify the mechanism of the diffuse phase transition. The temperature dependences of the Brillouin shift and full width at half maximum of the longitudinal acoustic mode show broad anomalies at the maximum temperature of the dielectric constant T m in all compositions. It indicates that elastic anomalies in NBT-xBT are caused by the coupling between the polarization and the strain. We consider this coupling is the piezoelectric coupling between the localized polarization in the polar nanoregion and the elastic strain. The composition dependence of the elastic constant in NBT-xBT at room temperature (T = 293 K) shows decreasing with approaching the morphotropic phase boundary (MPB) at about x = 0.06. It seems that the softening is reflected by the instability of the strain, as well as the polarization near the MPB.
0.5 )TiO 3 -xBaTiO 3 (x= 0.05, 0.08) are investigated by the broadband inelastic light scattering and the dielectric measurements. The dielectric constant shows a maximum at T m (the maximum temperature of a dielectric constant) where rhombohedral and tetragonal phases coexist. A central peak (CP) is clearly observed around T m by the inelastic light scattering measurements, and it indicates that the polarization relaxation plays a key role for the maximum of the dielectric constant. We consider that the broad one is attributed to the overdamped soft phonon, while the narrow one is related to the relaxation of the local polarizatio . We suggest two possible origins of the local polarization relaxation. n
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