In this study, lead-free (LiNaK)(NbTaSb)O 3 piezoelectric ceramics were fabricated on the basis of the amount of K 2 CO 3 addition, and their piezoelectric and dielectric properties were investigated by varying the amount of K 2 CO 3 addition and poling temperature. First, to achieve optimum poling conditions for manufactured specimens, the poling temperature was varied to be 0, 20, 50, 80, and 110 C. The optimum poling temperature was 20 C. It was found that 0.1 wt % K 2 CO 3 -added (Li 0:04 Na 0:44 K 0:52 ) (Nb 0:86 Ta 0:1 Sb 0:04 )O 3 ceramics exhibit excellent piezoelectric properties in an experiment performed on the basis of the amount of K 2 CO 3 addition. That is, a 0.1 wt % K 2 CO 3 -added specimen showed a large electromechanical coupling factor k p ¼ 0:494, a large piezoelectric constant d 33 ¼ 274 pC/N, and a high density of 4.65 g/cm 3 at the poling temperature of 20 C.
We present a detailed room temperature x-ray powder diffraction study on La2−xSrxNiO 4+δ with 0 ≤ x ≤ 0.12 and 0 ≤ δ ≤ 0.13. For x = 0.02, 0.04 and 0.06 the oxygen content phase diagrams of the Sr-doped samples show a similar sequence of pure phases and miscibility gaps as for pure La2NiO 4+δ . We find a weak Sr doping dependence of the δ range for the pure LTO, LTT and HTT phases; but overall, the δ ranges of the different phases do not vary strongly for x ≤ 0.06. Drastic changes are observed for x = 0.08 and 0.12, where miscibility gaps successively disappear. For x = 0.12 all oxygen-doped samples are in the HTT phase. The mechanism responsible for the suppression of the phase separation seems to involves multiple factors, including the Coulomb interaction between Sr impurities and interstitial oxygens as well as the reduction of the NiO6 octahedral tilt angle. The doping dependence of the lattice parameters shows clear differences for pure Sr and pure O doping. With the exception of the LTO phase, the in-plane lattice parameters explicitly depend on the type of dopant, rather than the net hole content, p = x + 2δ. In contrast, the orthorhombic strain in the LTO phase as well as the c-axis length appears to depend only on p; however, in the case of the c-axis length this "universal" behavior turns out to be accidental. Our results also show that the chemical pressure of La-site dopants is highly anisotropic, whereas that of O interstitials appears to be more isotropic. In general, this study reveals that Sr-doped samples have to be annealed carefully to achieve δ = 0, and to permit the study of the intrinsic properties of La2−xSrxNiO4.
Articles you may be interested inThe poling field and draw dependence of the piezoelectric and pyroelectric response of pressurequenched, phase I poly(vinylidene fluoride) films Some aspects of piezoelectricity and pyroelectricity in uniaxially stretched poly(vinylidene fluoride)The hydrostatic piezoelectric coefficient d p and the pyroelectric coefficient p y of poled unoriented phase I films were measured at pressures up to 7.0 Kbar and at temperatures from -84 to + 48 ·C. The pressure dependence of the glass transition temperature over the same pressure range was also determined. The results obtained for these unoriented films are compared with results obtained previously for oriented films. The effect of the glass transition temperature (Tg) and another transition occurring in the range of pressure and temperature used (T t ) on the piezoelectric and pyroelectric response for both oriented and unoriented films are discussed. At temperatures below T g , P y decreased with increased temperature, while d p showed a shallow maximum so that for both types of response minimum values were obtained at the T g •
Investigations of the dynamic piezoelectric response (d*31 and e*31) of unoriented poled poly(vinylidene fluoride) films containing different volume fractions of phase-I and phase-II crystalline materials show a linear relationship between phase-I content and piezoelectric response. Samples were poled under conditions (106 V/cm at 23 °C) which produced no observable changes in x-ray diffraction patterns taken before and after poling. The piezoelectric strain constant of the unoriented phase-II film is d′31=0.48×10−12 C/N, while that of the unoriented phase-I sample is d′31 =6.68×10−12 C/N. The data supports a model in which the piezoelectric activity is primarily due to a bulk polarization of the PVF2 by a 180° dipole switching mechanism in the polar phase-I crystals.
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