R. Von Der Muhll

Thick-film densification for pyroelectric sensors

Densification and adherence of thick films are usually achieved by the addition of a glass frit in the screen printing ink. However, the glass may have a detrimental effect on the electrical properties of the active component as a ferroelectric. The addition of a new step - the application of a uniaxial or isostatic pressure on the dry film - to the standard processing of thick films, enables one to obtain a good densification of the films, even without the use of glass. The efficiency of this new densification process of PZT-based films or `supported type microceramics is demonstrated. Pyroelectric properties of the screen printed layers are compared to those of ceramics of the same composition.

Dielectric and pyroelectric studies on the Ba1−3aBi2aTiO3 classical and relaxor ferroelectric ceramics

Low frequency dielectric studies in the temperature range 80–500 K were performed on the solid solution derived from BaTiO3, Ba1−3aBi2aTiO3 with 0<a<0.117. The temperature and frequency variations of the real part of the relative permittivity show two different behaviors, depending upon the substitution rate. A classical ferroelectric behavior was observed for a varying approximately from 0 to 0.03. However, a relaxor behavior appears for higher values of a. The replacement of Ba2+ by Bi3+ in the A site shows a remarkable decrease of TC. The dielectric studies were confirmed by pyroelectric study.

Dielectric and Raman studies on the solid solution (1−x)BaTiO3/xNaNbO3 ceramics

In order to elucidate the correlation between the relaxor type of phase transition and the percent of the A and B site substitution in the Ba1−xNaxTi1−xNbxO3 solid solution, the dielectric permittivity was carried out in the temperature range 80–600 K. All ceramics of these solid solutions present a ferroelectric–paraelectric phase transition with relaxor and classical character depending on the value of x. With increasing x the three phase transition of pure BaTiO3 are pinched into one rounded dielectric peak, and there is evidence for Vogel–Fulcher type relaxational freezing. Raman spectra of the x=0.3 and x=0.7 compositions taken at various temperatures and measured over the wavenumber range 100–1200 cm−1 confirm that the first order scattering is dominant in phonon bands resulting from both ordered region and disordered matrix.

Relaxor or classical ferroelectric behavior in ceramics with composition Sr2−xA1+xNb5O15−xFx (A = Na, K)

Abstract By partial cationic and anionic substitutions in NaNbO 3 –SrNb 2 O 6 and KNbO 3 –SrNb 2 O 6 systems, two solid solutions have been obtained: Sr 2− x Na 1+ x Nb 5 O 15− x F x and Sr 2− x K 1+ x Nb 5 O 15− x F x . They crystallize in the tetragonal tungsten bronze (TTB) type structure, which is related to that of the perovskite. The replacement of oxygen by fluorine causes a decrease of the Curie temperature. A weak F–O substitution rate increases the compactness, which leads to higher dielectric constant with good piezoelectric and pyroelectric characteristics. A relatively higher F–O substitution rate induces a ferroelectric relaxor behavior. Such relaxor ferroelectric ceramics with lead-free compositions can be of great interest for environment-friendly applications.

Piezoelectric and Pyroelectric Properties in Ferroelectric KTa0.3Nb0.7O3 Ceramics

Piezoelectric and pyroelectric properties of KT a0.3 Nb 0.7 O 3 ceramics which belong to the perovskite-ferroelectric ABO 3 family, were studied. The piezoelectric constants (d 31 = 18 pC/N, d 33 = 28 pC/N and d 15 = 19 pC/N) of these ceramics are higher than that for KNbO 3 . We found that the amplitudes of the fundamental frequency and its overtones for the thickness vibrations depend on the temperature in the ferroelectric phase. The value at room temperature of the pyroelectric coefficient (p = 10 nC cm -2 K -1 ) and the spontaneous polarization (P s = 35 μC cm -2 ) are in agreement with that of KNbO 3 .

Synthesis and physical study of LiTaO3-type flux-grown crystals

Abstract Stoichiometric LiTaO 3 - and oxyfluoride-related crystals, with a composition close to Li(Mg 0.05 -Ta 0.95 )O 2.85 F 0.15 were prepared by a flux-growth method. The crystals were studied by X-ray diffraction, optical, dielectric and pyroelectric measurements. The birefringence and the dielectric losses at room temperature are lowest for the oxyfluoride crystals. Both birefringence and ferroelectric Curie temperature values were correlated.

Etudes physico-chimiques d'une nouvelle phase hydroxofluoree ferroelectrique de type LiTaO3

Abstract New LiTaO 3 -type ferroelectric hydroxofluoride phases belonging to the LiTaO 3 -“LiMgF 3 ”-“LiMg(OH) 3 ” system have been prepared by solid state reaction. The strongly densified ceramics show increased permittivity near the phase transition temperature, the value of which rises with the OH - concentration.

Investigation of ferroelectric and pyroelectric properties of ceramics with composition Ba(Li/sub 2x/Al/sub 2-2x/)O/sub 4-4x/F/sub 4x/ (0<or=x<or=0.03)

The structural, ferroelectric, pyroelectric, and dielectric relaxation properties of ceramics with composition Ba(Li/sub 2x/Al/sub 2-2x/)O (0<or=x<or=0.3) have been investigated. XRD (X-ray diffraction) patterns show a lattice close to that of BaAl/sub 2/O/sub 4/. The parameters increase with increasing x up to x=0.1 and then remain constant. The Curie temperature T/sub C/ decreases regularly from T/sub C/=396 K (x=0) down to T/sub C/=324 K (x=0.1) and then increases again with x up to T/sub C/=460 K (x=0.3). The values of the spontaneous polarization P/sub s/ are in the range 1-22 nC-cm/sup -2/. The solid solutions seem to be of weak ferroelectric type with a maximum of P/sub s/ around 200 K and low values of in /sub r/, the pyroelectric coefficient, and P/sub s/. Dielectric relaxation is detected for Ba(Li/sub 0.4/Al/sub 1.6/)O/sub 3.2/F/sub 0.8/ with a relaxation frequency from 10/sup 2/ to 10/sup 4/ Hz between 300 and 520 K. A model accounting for weak ferroelectricity is proposed.<<ETX>>

New ferroelectrics Ba/sub 1-x/M/sub x/ (Li/sub 2x/Al/sub 2-2x/) O/sub 4-4x/F/sub 4x/ (M=Pb,Sr)

New ferroelectric ceramics Ba/sub 1-x/M/sub x/(Li/sub 2x/Al/sub 2-2x/) O/sub 4-4/F/sub 4x/ with x in (0,0.07) for M=Pb and x in (0.0.1) for M=Sr have been studied. The behavior of T/sub c/ with composition has been determined. For Pb T/sub c/ decreases from 396 to 233 K when x rises from 0 to 0.04, and then, when x rises from 0.04 to 0.07, T/sub c/ increases from 233 to 320 K. The thermal variation of P/sub s/ (spontaneous polarization) has also been determined. The variation of T/sub c/ for the Sr compound is rather similar: T/sub c/ decreases first from 396 to 238 K when x rises from 0 to 0.05 and then remains constant when x increases up to 0.1.<<ETX>>

Optical characteristics of Pb/sub 5/Al/sub 3/F/sub 19/-type crystals

Large colorless crystal of the Pb/sub 5/Al/sub 3/F/sub 19/ type with dimensions approaching 1 cm/sup 3/, have been grown in sealed platinum tubes by the Bridgman technique. The phase transitions in Pb/sub 5/Al/sub 3/F/sub 19/ have been studied by optical microscopy on crystals oriented along different crystallographic directions. Ferroelastic domains have been observed; a reversible and reproducible ferroelastic-prototype transition has been shown. The thermal dependence of the birefringence has also been studied. The ferroic properties of Pb/sub 5/Al/sub 3/F/sub 19/ are discussed in relation to the crystal symmetry.<<ETX>>