Search

Mechanical, piezoelectric and dielectric properties of PZT ceramics (Pb 0.98 M 0.02 [(Zr 0.535 Ti 0.465 ) 0.995 ]O 3 , M=Er, Gd, Eu, Nd, La and Bi) have been studied. The fraction of A sites occupied by the different additives is estimated and is found to increase with the ionic radius of the additive ion. The density is high in Bi-, Gd- and Eu-PZT samples. Small amounts of the pyrochlore phase are present in Gd- and Eu-PZT. A maximum strength of 80–100 MPa and K IC of ∼1.5 MPa m 1/2 are obtained in Gd- and Eu-PZT. The R -curve behavior becomes more pronounced in Gd- and Eu-PZT, and it is observed that the strength and K IC increase with the slope of the K IC versus c 1/2 plot. Very good piezoelectric properties, i.e. d 33 of 410 PCN −1 , dielectric constant of 1005, κ p of 0.49 and the hydrophone figure of merit, d h g h , of 2760 are obtained for Nd-PZT. The piezoelectric properties in Bi-PZT are also higher than for the undoped composition, while for the Gd-PZT, these are slightly inferior. For all other compositions, the piezoelectric properties are not affected much.

Lead zirconate titanate ceramics having composition at the morphotropic phase boundary have been modified with 2 mol % rare-earth oxides of Er, Gd, Eu, Nd and La. The samples have been prepared using the standard solid state reaction route. The ionic radius of the additives investigated vary from 0.088 to 0.106 nm. A theoretical model has been used which allows the additive cation distribution between A and B sites to be established from its ionic radius. It has been concluded that the additive goes increasingly to the A site with increasing ionic radius. The amounts of lead monoxide liberated during sintering due to incorporation of the additives have been studied. Using this PbO loss data the distribution of the additive between A and B sites has been calculated. It has been observed that the experimental results agree well with theoretical calculations.

Single phase lead zirconate titanate (PZT) of tetragonal structure (Zr:Ti=0.40:0.60) was modified using a trivalent rare earth additive Nd 2 O 3 . The samples having composition Pb 1-(3x/2) Nd x (Zr 0.40 Ti 0.60 )O 3 was prepared by solid state route. The Nd content in the samples was varied from 0–4 mol %. The effect of Nd 3+ additive on mechanical and electrical properties of PZT ceramics has been studied. It was observed that Nd addition results in enhancement of fracture toughness ( K IC ) and Vicker’s hardness ( H v ) in the samples. Nd addition also results in substantial increase in dielectric constant and d 33 piezo coefficient of PZT ceramics. The maximum value of K IC obtained is 2.05 Mpam 1/2 . Also the peak value of 680 for dielectric constant and a d 33 of 240 pCN −1 is obtained for the same composition. Both the mechanical and electrical properties seem to peak at 2% Nd 3+ addition, which makes this composition attractive for actuator and other high power ultrasonic transducer applications. The increase in mechanical properties has been attributed the increased tetragonality (c/a ratio) and increase in sintered density with Nd addition. It seems that the ferroelastic domain switching is the main contributor to toughening in these ceramics. The increased tetragonality with Nd addition results in more work done in domain switching and, hence, enhanced toughness. The increase in electrical properties with Nd addition has been attributed to reduction in oxygen vacancies in the samples. The X-ray and the sintered density results also suggest that at 2 mol % Nd addition, Nd is reaching its solubility limit in PZT system.

The effect of net PbO content (obtained by taking into account the amount of excess PbO added and PbO loss during sintering) on the mechanical and piezoelectric properties of lead zirconate titanate (PZT) ceramics has been studied. The samples were prepared by the solid state route using the morphotropic phase boundary composition Pb(Zr 0.535δ Ti 0.465 )O 3 . Excess PbO was also added to the samples in varying amounts from 0–1.0 wt.%. To vary PbO volatility the samples were sintered with and without a PbO rich atmosphere at 1220°C for 2 h. The resulting Pb content as given by x in Pb 1+ x (Zr 0.535 Ti 0.465 )O 3+ x varied from x =−1.7×10 −2 to 1.8×10 −2 . The sintered density was found to increase with increasing lead content. The precipitation of the second phase believed to be ZrO 2 is observed for x =−1.7×10 −2 . The fracture mode changed from intergranular to transgranular with increasing x . The fracture toughness ( K IC ) and strength are minimum near x =0 and increase with increasing as well as decreasing x . The maximum values of K IC and strength are 1.45 MPa m 1/2 and 90 MPa, respectively, for x =1.8×10 −2 . The dielectric constant and piezoelectric strain coefficient d 33 increased with x .

The present study is an investigation of the structural and electrical properties of solid solution processed lead zirconate titanate (PZT) ceramics modified by CeO2. The PZT composition studied is Pb(Zr0.535Ti0.465)O3 modified with 0.0–0.2 mol % CeO2. Studies of the loss of lead oxide during sintering have been performed. The lead loss increases with increasing Ce in the sample up to 0.1 mol % Ce and becomes nearly constant on further addition of Ce. The lattice parameters and cell volume of the tetragonal phase of PZT also increase with addition of Ce up to 0.1 mol % Ce. The lead loss and X-ray data indicate that Ce is being reduced to Ce3+ and is going onto the A-site of the PZT perovskite system. The study concludes that controlled modification of the MPB composition of PZT using 0.1 mol % CeO2 results in substantial enhancement of piezoelectric strain coefficients, dielectric constant and electromechanical coupling coefficients.

Aspirin is a highly successful antiplatelet drug & still retains its status as the \'front-line\' antiplatelet drug; however, increased understanding of platelet biology has led to the development of new antiplatelet drugs that are potentially more effective. Now, more researches in platelet biology has led to this fact that there are more than 90 other metabolic pathways leading to platelet aggregation that are independent of arachidonic acid and therefore not inhibited by aspirin, hence, several more drugs are being developed, aimed at controlling different phases of platelet function such as platelet aggregation & adhesion. The newer drugs now offer potentially greater and more specific control over platelet function. Definitely, these drugs are going to be significantly more expensive than aspirin, and their eventual role in the clinical arena will ultimately depend on both their efficacy and their cost-effectiveness. As we approach the next millennium, it is envisaged that our increased understanding of platelet function, coupled with advances in technology and drug manufacture, will result in even greater improvements in the therapeutic control of platelet thrombus.