Polar Glass-ceramics Research Articles

Sr2TiSi2O8 (STS) Polar Glass-Ceramics: Effect of Na2O and CaO Additions in the Parent Glass on the Crystallization Mechanism and on the Piezoelectric Properties

Glass-ceramics containing pyroelectric Sr2TiSi2O8 (STS) crystals are produced from parent glasses of compositions STS + 0.8 SiO2 + (0.2 − x) Na2O + x CaO, with x = 0; 0.05; 0.10; and 0.15. The aim of this work is to investigate the effect of the additions to the stoichiometric STS composition on the crystallization mechanisms and on the piezoelectric properties of the glass-ceramic. The DSC analyses evidence that the glass transition temperatures Tg, the onset temperature of the crystallization peak To and the temperature Tc of the maximum of this peak increase with the CaO/Na2O ratio. On the basis of the DSC data, the crystallization of the parent glass samples was operated by thermal treatment. The observation of the cross-sections of the heat-treated samples highlights that the competition between the surface and volume crystallization mechanisms is influenced by the CaO/Na2O ratio and the temperature. For all the samples, the XRD analyses performed on the surfaces as obtained after the crystallization treatment evidenced a preferential orientation of the STS crystals with the plans (00l) parallel to the surface. The XRD analyses performed after grinding the surface show that only the surface crystallized layers are preferentially oriented. Moreover, changes in preferential orientation to plans (202) or (201) are observed over the depth, depending on the composition and the temperature of the thermal treatment. These changes influence the polarization of the surface crystallized layer and, consequently, its piezoelectric charge coefficient d33. The highest values of d33 were measured on the glass-ceramic samples exhibiting mainly a (202) preferential orientation over their thickness.

Polar glass-ceramics for piezocatalytic applications

Glass-ceramics containing oriented Sr2TiSi2O8 fresnoite crystallites were explored for piezocatalysis induced dye degradation capability. The parent glass of the 2SrO–1TiO2–3.3SiO2–0.2K2O–0.1Al2O3 (components are indicated by molar ratio) composition was manufactured using the well-known melt-quench method. The two-parent glass samples were separately heat-treated at the crystallization temperature of 850 and 1000 °C/3 h for obtaining varying amounts of Sr2TiSi2O8 crystallites in the glass matrix. The presence of Sr2TiSi2O8 crystallites on the surface of both glass-ceramics was confirmed using x-ray diffraction. The micrographs obtained from the scanning electron microscope evidenced the presence of more numbers along with the greater sizes of Sr2TiSi2O8 crystallites on the surface of the 1000 °C/3 h sample in comparison to the 850 °C/3 h sample. These glass-ceramics were piezoelectric, as the 1000 °C/3 h sample showed a maximum d33 value of 10 pC/N after sufficient polishing. This non-ferroelectric piezoelectricity was induced due to the oriented crystallization of Sr2TiSi2O8 crystallites in the glass-ceramics. The transparency was decreased in this order: parent glass>850 °C/3 h sample>1000 °C/3 h sample. During the piezocatalytic dye degradation experiment, the degradation of methylene blue dye was found to be 71% and 83% within 300 min under ultrasonication energy using 850 and 1000 °C/3 h glass-ceramics, respectively. The hydroxyl radical (OH˙) was identified as the main active species behind the piezocatalytic dye degradation using glass-ceramics. Hence, this work showed that glass-ceramics can be used for the water-cleaning application using vibrational energy.

Effect of Partial Ba Substitutions on the Crystallization of Sr2TiSi2O8 (STS) Glass-Ceramics and on the Generation of a SAW Signal at High Temperatures.

Because of their characteristics, including a d33 of 10–15 pC/N and high stability up to temperatures over 1000 °C, polar glass–ceramics containing fresnoite crystals can be regarded as highly effective materials for applications requiring piezoelectricity at high temperatures. In the present paper we investigate barium substitutions in an Sr-fresnoite (STS) glass–ceramic. Two aspects are studied: first, the effect of the substitution on the preferential orientation of the crystallization, and second, the ability of the glass–ceramics to generate and propagate surface acoustic waves (SAW) at high temperatures. XRD analyses show that a 10 at.% substitution of Ba allows us to keep a strong preferential orientation of the (00l) planes of the fresnoite crystals down to more than 1 mm below the surfaces. Higher substitution levels (25 and 50 at.%), induce a non-oriented volume crystallization mechanism that competes with the surface mechanism. SAW devices were fabricated from glass–ceramic substrates with 0, 10 and 25 at.% Ba substitutions. Temperature testing reveals the high stability of the frequency and delay for all of these devices. The glass–ceramic with a 10 at.% Ba substitution gives the strongest amplitude of the SAW signal. This is attributed to the high (00l) preferential orientation and the absence of disoriented volume crystallization.

Enhancement in pyroelectricity of polar Ba0.9Sr0.1TiO3 –TeO2 glass-ceramics

In the present work, the piezoelectric and pyroelectric properties of lead free ferroelectric Ba0.9Sr0.1TiO3 ceramic are altered with the addition of TeO2 glass ceramics. For this, crystalline phase of γ- TeO2 prepared by melt-quench method is mixed with Ba0.9Sr0.1TiO3 prepared by solid state reaction method, to form compounds (1-x)Ba0.9Sr0.1TiO3 – (x) TeO2, x = 0 – 0.1 at the steps of 0.025. The structural and impedance analyses confirm formation of solid solution up to x ≤ 0.05 and thereafter they show composite formation. The dielectric permittivity is observed to be maximum for composition x = 0.075. The XPS and EDX analyses are showing highest oxygen vacancy at x = 0.05. The piezoelectricity is measured using Piezo Force Microscopy technique and c-axis domains are observed showing the formation of polar glass-ceramics. The pyroelectric current increases with the increase in TeO2 content, showing the suitability of samples for energy harvesting and pyroelectric detectors.

Field-Assisted Isothermal Oriented Crystallization of SrO-TiO<sub>2</sub>-SiO<sub>2</sub> Polar Glass-Ceramics

The polar glass-ceramics of 2.0SrO-1.0TiO2-2.9SiO2 system were prepared by the process of recrystallization with additional applied isothermal and electric field. The results showed that the glass-ceramics piezoelectric constant d33 was 12×10-12 C/N. The study of its oriented crystallization by SEM and XRD indicated that Sr2TiSi2O8 crystal performed oriented growth, which was perpendicular to the glass surface and made it be orientally crystallized with the assisted the isothermal and electric field. The further experimental results showed that the additional electric field reduced the crystallization activation energy, which provided a force for the isothermal orientating crystallization process.

Ferroelectric and Nonferroelectric (Polar) Piezoelectric Glass–Ceramics

An increased need for high‐temperature piezoelectric materials for sensors, some of which must be Pb free due to RoHS regulations, has led to a focused search for suitable materials. Glass–ceramic processing—the controlled crystallization of a precursor glass—offers a unique manner in which to produce partially to wholly crystalline, Pb‐free, and temperature‐stable piezoelectric materials starting with optically homogeneous amorphous materials. Building on previously published work, we have produced NaNbO3‐containing, poled, and pore‐free ferroelectric glass–ceramics that exhibit d33 values of ∼15 pC/N, a dielectric constant of ∼200, an Np frequency constant of ∼3400 Hz·m, and Qm∼60. Nonferroelectric, lithium borosilicate polar glass–ceramics—initially developed by R.E. Newnham and coworkers at Penn State some 20 years ago—have also been produced and yielded d33 values of ∼5 pC/N, although with dielectric constants of <10 they achieved significant g33 values (∼50 × 10−3 V m/N; Np∼4500 Hz·m; Qm∼1500). Room‐temperature planar coupling coefficients of 0.15 and 0.10 were obtained for the polar and ferroelectric varieties, respectively. High‐temperature resonance measurements of both varieties reveal piezoelectricity to at least 600°C for the polar glass–ceramic and up to 300°C for the ferroelectric variety. Excessive conductivity in the polar type, presumably due to high lithium contents, resulted in a strong decrease in resonance amplitude as the temperature was increased. Interestingly, the estimated piezoelectric coefficients for this type showed nearly no temperature dependence and suggest that polar glass–ceramics, lacking a Curie temperature, potentially offer a unique route to high‐temperature piezoelectrics.

Effect of internal electrostatic field on isothermal orientation of barium titanium silicate polar glass-ceramics

Our experiment has shown that a grain-oriented structure can be obtained in barium titanium silicate glass ceramics under an isothermal orientation process, without temperature gradient or electric field. A dipole model was developed originally to simulate the isothermal oriented crystallization of BTS glass. Due to the internal electrostatic field induced by the polar crystallites, the additive energy to the crystallization of BTS glass derived from the dipole model is as high as 0.35 eV. Compared with the crystallization activation energy of 2.39 eV, the internal electrostatic field plays a significant role in the crystallization process, which leads to a change in the rates of crystal growth in different directions and a grain-oriented structure.

Grain oriented crystallization, piezoelectric, and pyroelectric properties of (BaxSr2−x)TiSi2O8 glass ceramics

Polar, nonferroelectric (BaxSr2−x)TiSi2O8 glass ceramics with highly oriented crystallites were prepared by a gradient temperature heat treatment technique. The crystallization mechanism and microstructures of (BaxSr2−x)TiSi2O8 glass ceramics were investigated by means of differential thermal analysis, x-ray diffraction and scanning electron microscopy, and the dielectric, piezoelectric and pyroelectric properties were investigated for various compositions. The results show that polar (BaxSr2−x)TiSi2O8 glass ceramics have a low dielectric constant and a high hydrostatic figure of merit dh×gh=∼2500. This high hydrostatic figure of merit, along with other unique characteristics, such as no aging or depoling problems and good stability at high temperatures, high pressure, and in harsh environments, makes (BaxSr2−x)TiSi2O8 glass ceramics attractive for use as hydrophones and high temperature infrared detectors.

Study on the dielectric property of diphasic polar glass-ceramics

A new kind of the oriented polar glass—ceramics i.e. the diphasic polar glass—ceramic (Sr2TiSi2O8 and SrTiO3) is first prepared. This unique material shows the piezoelectric property of Sr2TiSi2O8 crystal and the high dielectric property of SrTiO3 crystal.

Polar glass ceramics

Abstract Recent work has shown that piezoelectric and pyroelectric ceramics having oriented crystallites can be fabricated by the directional crystallization of a glass of a selected composition. Although the requirement for an absence of a crystallographic center of symmetry restricts the choice of materials available for this process the major restrictions are set by processing limitations rather than by composition, e.g. suitable piezoelectric precursors in glass, ability to crystallize the glass in a controlled manner, adjustment of appropriate crystallographic axes of the crystallites, etc. Candidate glass compositions can be prepared from but not limited to the systems Li2O-SiO2, Li2O-B2O3-SiO2, Li2O-B2O3, BaO-SiO2-TiO2, BaO-GeO2-TiO2 and so on. Such oriented glass ceramics have pyroelectric, piezoelectric and bulk acoustic wave electromechanical properties comparable to their single crystal form. This paper reviews the potentiality of glass ceramics for the infrared sensors, bimorphs, hydrophones, surface acoustic wave substrates, FOEMA (fiber optic electromagnetic antenna) and other related sensor applications. When the nucleation process in the glass is suitably controlled the glass ceramics with high transparency are produced. Also for the suitable compositions large optical SHG signals are observed.

Piezoelectricity, pyroelectricity and ferroelectricity in glass ceramics based on PbTiO 3

Piezoelectric, pyroelectric and ferroelectric glass ceramics of the PbOTiO 2Al 2O 3SiO 2 system with the addition of other oxides have been studied. A piezoelectric resonance in a freely-suspended sample according to its thickness extension vibration mode is observed. The dielectric, piezoelectric, electromeemical coupling and other parameters, including d 33 = 40 × 10 −12C/N, ϵ 33 T / ϵ 0 = 60, g 33 = 80 × 10 −3 m · V/N, k t = 0.225, are measured. The pyroelectric responses, with the characteristics p = (10−22)× 10 −9 C/cm 2 K, have good linearities from room temperature to nearly 200°C. The existence of ferroelectricity, which gives the most important precondition of the piezoelectricity and pyroelectricity after poling, is verified through: (1) the hysteresis loops by Sowyer-Tower circuit, (2) the ferroelectric domains by TEM, (3) the perovskite-type of ferroelectric crystalline phase PbTiO 3 solid solution by XRD, (4) the abnormality of transition between ferroelectric phase and paraelectric phase, as well as (5) the normalized mode based on an IR absorption band referred to the ferroelectric soft mode of Ti I bond stretching vibration. This material is different either from the corresponding ceramics and single crystals or from non-ferroelectric polar glass ceramics and isotropic gglass ceramics containing ferroelectric crystalline phases. The new characters and features have also been discussed.

Unusual pyroelectric and piezoelectric properties of fresnoite (Ba2TiSi2O8) single crystal and polar glass-ceramics

The dielectric, piezoelectric and pyroelectric properties of fresnoite (Ba2TiSi2Os) single crystal and polar glass-ceramics were studied in the temperature range - 150 to 200°C. The sign of pyroelectric coefficient is positive at room temperature and becomes negative at 190°C. The dielectric constant, pyroelectric coefficient and planar coupling coefficient show a maximum value at 160°C and the frequency constant shows a minimum at the same temperature. The probable reasons for the anomaly in these properties are discussed.

New Materials for Hydrophone Applications- Single Crystals and Polar Glass-Ceramics

Hydrostatic piezoelectric strain coefficients dh (∼10 pC/N) and voltage coefficients gh (80–100×10-3 V m/N) on single crystals of Ba2TiSi2O8, Ba2TiGe2O8 have been measured as a function of temperature, pressure, and frequency. The values are found to be comparable to those of the state of the art piezoelectric PVDF polymers. Measurements are also made on the glass-ceramics in the compositions of BaO–TiO2–SiO2 and some isostructural materials compositions in the system BaO–TiO2–GeO2. The typical values of the piezoelectric constants of glass ceramics are almost on the order of those obtained on the respective single crystal samples. Glass-ceramics provide a promising way of achieving the larger area samples needed for various piezoelectric devices.

A new family of grain orinted glass-ceramics for piezoelectric and pyroelectric devices

Abstract Grain oriented polar glass-ceramics have been evaluated for application in piezoelectric and pyroelectric devices. The main advantage of the method is the possibility of preparing large area elements in a simple way at a relative low cost.

Polar glass ceramics for sonar transducers

Glass ceramics are shown in this study to be a new class of transduction materials for application in sonar transducers. It is found that glass ceramics of Ba2TiSi2O8 have high hydrostatic voltage sensitivity, low dielectric loss, and low dielectric constant. These properties are also shown to be practically independent of pressure up to 35 MPa. The free-field voltage sensitivity of a glass-ceramic prototype hydrophone is higher than that based on a commonly used lead zirconate titanate ceramic element.

Polar glass ceramics — A new family of electroceramic materials: Tailoring the piezoelectric and pyroelectric properties

Grain oriented multicomponent polar glass-ceramics have been prepared by crystallizing the glasses in a temperature gradient. Inexpensive, large area piezoelectric and pyroelectric devices can be fabricated by this method, and by adjusting the composition of the glasses and crystallization conditions, it is possible to tailor the properties to meet device requirements. Based on the growth characteristics and the connectivity pattern of the crystallites, the piezoelectric, pyroelectric and dielectric properties of glass-ceramic composites can be predicted. Two examples discussed in this paper are piezoelectric glass-ceramics which are not pyroelectric, and pyroelectric glass-ceramics which are not piezoelectric.

Polar glass ceramics

Abstract Pyroelectric-piezoelecric glass ceramics of polar materials like Li2Si2O5, Ba2TiGe2O8, Ba2TiSi2O8, and Various compositions in the systems Li2O-B2O3, Li2O-SiO2-ZnO, Li2O-SiO2-B2O3 have been prepared by oriented recrystallization of the glasses under a strong temperature gradient, providing a simple inexpensive process for preparing piezoelectric and pyroelectric materials. High pyroelectric responses were observed in these glass-ceramics. Values of piezoelectric d33 coefficients, frequency constants, electromechanical coupling coefficients and dielectric properties of glass-cermics were in close agreement with the values of respective single crystals.