Marina Villegas

Temperature Sensing with Up-Converting Submicron-Sized LiNbO3:Er3+/Yb3+ Particles

We present the temperature dependence of the green up-converted luminescence in submicron-sized LiNbO3:Er3+/Yb3+ particles in the range between 12 and 180 °C. It is shown that LiNbO3:Er3+/Yb3+ exhibits a very high sensitivity (S = 0.007/°C at physiological temperature and a maximum value of S = 0.014/°C at 350 °C) that surpasses those previously found for other materials based on Er3+/Yb3+ luminescence, indicating that LiNbO3:Er3+/Yb3+ is a suitable probe for optical temperature sensing through the fluorescence intensity ratio technique. This high sensitivity can be explained using the intrinsic spectroscopic parameters of Er3+ ions in this host.

Electrophoretic Deposition of Flake-Shaped ZnO Nanoparticles

ZnO films have been grown on different substrates by using a variety of fabrication techniques. In the present work, we discuss the results on the preparation of ZnO films by electrophoretic deposition (EPD) starting from synthetic flake-shaped nanoparticles. The critical parameters related to the preparation of aqueous colloidal suspensions have been analyzed. Dispersing conditions have been evaluated in terms of particle/cluster morphology, electrokinetic properties, i.e., particle size distribution and cationic surface functionality, and zeta potential. EPD parameters for film assembly have been selected. Depending on both the particle morphology and the solids concentration in the colloidal system, different orientation effects have been observed in the built structure. For a low ZnO concentration, independent clusters arrive at the Ni substrate where the large dimension of the ZnO flakelike nanoparticles align with the surface of the substrate. When the solids concentration increases, such ordering is not observed. The electrical resistivity measured by the four-point probe method evidences the presence of a ZnO film with unusually high electrical resistivity for undoped ZnO.

Processing and dielectric properties of the mixed-layer bismuth titanate niobate Bi7Ti4NbO21 by the metal-organic precursor synthesis method

Abstract The preparation of homogeneous Bi 7 Ti 4 NbO 21 single phase nanosized ceramic powders at temperatures as low as 400–500°C using a metal-citrate complexes method, based on the Pechini-type reaction route, is described. The thermal decomposition/oxidation of the polymerized resin, as investigated by TG/DTA, XRD, Raman spectroscopy and SEM, led to the formation of a well defined orthorhombic Bi 7 Ti 4 NbO 21 compound with lattice parameters a =0.544, b =0.540 and c =2.905 ± 0.0005 nm. Reaction formation takes place through an intermediate binary phase with a stoichiometry close to Bi 20 TiO 32 which forms between 300 and 375°C. The metal-organic precursor synthesis method, allows the control of the Bi/Ti/Nb stoichiometric ratio leading to the rapid formation of the nanosized bismuth titanate niobate, Bi 7 Ti 4 NbO 21 , ceramic powders, at temperatures much lower than usually needed in the conventional route. Sintering of the as-prepared ceramic powders led to near full density samples in the temperature range 1100–1130°C. The mixed-layer structure Bi 7 Ti 4 NbO 21 ceramics showed two phase transitions at about 650 and 850 ± 5°C, and a piezoelectric modulus, d 33 , as high as 20×10 −12 C/N.

Evaluation of Piezoelectric Properties of Bi4Ti3O12—Based Ceramics at High Temperature

Nowadays many industries as aeronautic, aerospace, etc, are claiming for new sensors and actuators that can operate in hostile environments. PZT ceramics are the common materials used in piezoelectric devices, however their low Curie temperature prevents their use at high temperatures. Bi4Ti3O12-based ceramics show a great potential for high temperature applications. Although piezoelectric parameters of BIT ceramics are well described at room temperature, its behaviour at high temperatures is almost lacking. This paper describes an experimental set-up to measure the piezoelectric properties of high temperature piezoceramics up to 700°C. The variation of piezoelectric parameters of W-doped BIT ceramics as a function of temperature indicates that their operating temperature extends up to 500°C, surpassing the expected one (½ Tc) in more than 200°C.

Vibration characteristic of cymbal type transducers

A cymbal transducer consists of a poled piezoelectric disk which is sandwiched between two metal endcaps, each containing a truncated cone-shaped cavity. Three different designs, an asymmetric cymbal, a symmetric cymbal and a thimble, were produced and their frequency responses were studied. The main vibration modes were identified and the frequency tunability by external mass addition was demonstrated.

Reactive sintering of phosphorous coated BaTiO3

Abstract Doping BaTiO 3 with P 5+ has been reported to decrease the sintering temperature of the ceramic, allowing homogeneous fine grained microstructures to be obtained. According to the present paper, the formation of a phosphorous-BaO rich phase covering the BaTiO 3 particles seems to be the origin of the improved porosity coalescence and removal observed at the earlier sintering stage of these materials. The formation and development of phosphorous-barium rich phases have been followed by means of DRX, and high temperature NMR. Phosphorous cations incorporated from phosphate ester form a surface layer covering the BaTiO 3 particles which reacts during heating to form Ba 2 TiP 2 O 9 and/or Ba 3 (PO 4 ) 2 . Formation of these phases seem to occur by solid-solid reaction involving phosphorous diffusion through the BaTiO 3 particles.

Influence of the LiNbO3 and KNbO3 seeds on the sintering and electrical properties of PMN ceramic

The effect of LiNbO 3 and KNbO 3 seeds on the microstructure and dielectric characteristics of PMN ceramic prepared by columbite route have been investigated with the addition of 0, 1, and 2-wt% of seeds. X-ray diffraction, Scanning Electron Microscopy and an impedance analyzer were used to characterize the influence of seeds on physical characteristics and dielectric properties of PMN. LiNbO 3 -seeded PMN samples present a significant increase in the amount of perovskite phase. The addition of LiNbO 3 seeds in sintered PMN ceramics at 1100@C during 4 h causes a decrease in the porosity and the amount of pyrochlore phase. Weight losses during sintering of PMN ceramics are suppressed more significantly for LiNbO 3 -seeded PMN. T m of PMN ceramics changes with seeds concentration. KNbO 3 seeds displace T m to lower temperature whereas LiNbO 3 causes its elevation. Dielectric constants of approximately 13,000 at 1 kHz was measured at m 5°C in PMN ceramics with 1-wt% of LiNbO 3 seeds.

Low temperature synthesis of bismuth titanate niobate nanoparticles from polymeric precursor

Abstract The preparation of homogeneous Bi7Ti4NbO21 single phase ceramic nanosized powders at temperatures as low as 400°− 500°C using a metal-citrate complexes method, based on the Pechini-type reaction route, is described. The thermal decomposition/oxidation of the polymerized resin, as investigated by TG/DTA, XRD, and SEM, led to the formation of a well defined orthorhombic Bi7Ti4NbO21 compound with lattice parameters a=0.544, b=0.540, and c=2.905 ± 0.0005 nm. Reaction formation take place through an intermediate binary phase with a stoichiometry close to Bi20TiO32 which formes between 300°C and 375°C. The metal-organic precursor synthesis method, allows to control the Bi/Ti/Nb stoichiometric ratio leading to the rapid formation of the nanosized bismuth titanate niobate, Bi7Ti4NbO21, ceramic powders, at temperatures much lower than usually needed in the conventional route.