Piezoelectric and acoustic properties of potassium titanyl phosphate (KTP) and its isomorphs

The bulk elastic and piezoelectric properties of potassium titanyl phosphate (KTP) and some of its family members such as RbTiOPO(4 ) (RTP) and RbTiOAsO(4) (RTA) have been determined. The piezoelectric, elastic, and dielectric matrix (P-E-D) of KTP has been completely characterized. Values for the temperature dependence of the expansion coefficients and elastic constants have been obtained, and the effects of variations in dielectric constant on coupling coefficient determined. The major diagonal elements of the piezoelectric and elastic matrices of RTP and RTA were measured as were the thermal expansion coefficient of all the KTP isomorphs, KTP in the temperature range 25-80 degrees C, is shown to have a combination of large coupling coefficients (up to k(t)=38% for hydrothermally grown KTP) and medium temperature dependence coefficients of elastic constant (as low as 40 p.p.m./ degrees C for tau(c33) for hydrothermally grown KTP) that makes it attractive for many piezoelectric applications.     

Integrated-optical wavelength sensor with self-compensation of thermally induced phase shifts by use of a LiNbO3 unbalanced Mach-Zehnder interferometer

We demonstrate an integrated-optical unbalanced Mach-Zehnder interferometer in lithium niobate for detecting wavelength shifts of light sources, such as laser diodes and superluminescentdiodes at lambda = 844 nm. The output signal can be used to stabilize the light source. Because of the temperature dependence of the effective refractive index and the thermal expansion of the substrate, the device acts also as a temperature sensor. The temperature sensitivity of the interferometer was compensated for by the combination of proton exchanged- and annealed proton exchanged-channel waveguides by approximately two orders of magnitude. The thermo-optic coefficients of the extraordinary effective refractive index in integrated optical channel waveguides in LiNbO8 have been measured with high accuracy over a temperature range from 10 degrees C to 40 degrees C.     

Measurement of linear thermal expansion coefficient of alkali-activated aluminosilicate composites up to 1000 °C

The effect of high temperatures up to 1000 °C on the length changes of two alkali-activated aluminosilicate composites, one of them with quartz sand aggregates, the second with electrical porcelain, is analyzed in the paper. The thermal strain vs. temperature functions of both materials are found to increase monotonically in the whole temperature range studied so that the thermal expansion mismatch (the gel undergoes thermal shrinkage, the aggregates expand with increasing temperature) results in positive values of the apparent linear thermal expansion coefficient. The composite material with electrical porcelain aggregates exhibits a more desired thermomechanical behavior which is a consequence of the better high-temperature thermal stability of electrical porcelain as compared to quartz. In a comparison with Portland-cement based composites, the linear thermal expansion coefficient of both studied aluminosilicates is substantially lower in the whole temperature range of 20–1000 °C.     

Optical temperature sensor and thermal expansion measurement using a femtosecond micromachined grating in 6H-SiC

An optical temperature sensor was created using a femtosecond micromachined diffraction grating inside transparent bulk 6H-SiC, and to the best of our knowledge, this is a novel technique of measuring temperature. Other methods of measuring temperature using fiber Bragg gratings have been devised by other groups such as Zhang and Kahrizi [in MEMS, NANO, and Smart Systems (IEEE, 2005)]. This temperature sensor was, to the best of our knowledge, also used for a novel method of measuring the linear and nonlinear coefficients of the thermal expansion of transparent and nontransparent materials by means of the grating first-order diffracted beam. Furthermore the coefficient of thermal expansion of 6H-SiC was measured using this new technique. A He-Ne laser beam was used with the SiC grating to produce a first-order diffracted beam where the change in deflection height was measured as a function of temperature. The grating was micromachined with a 20 microm spacing and has dimensions of approximately 500 microm x 500 microm (l x w) and is roughly 0.5 microm deep into the 6H-SiC bulk. A minimum temperature of 26.7 degrees C and a maximum temperature of 399 degrees C were measured, which gives a DeltaT of 372.3 degrees C. The sensitivity of the technique is DeltaT=5 degrees C. A maximum deflection angle of 1.81 degrees was measured in the first-order diffracted beam. The trend of the deflection with increasing temperature is a nonlinear polynomial of the second-order. This optical SiC thermal sensor has many high-temperature electronic applications such as aircraft turbine and gas tank monitoring for commercial and military applications.     

Semiempirical Estimation of Thermal Expansion Coefficients and Isobaric Heat Capacities of Fluorite-Type Compounds

The thermal expansion coefficients and isobaric heat capacities of fluorite-type compounds have been estimated using the Morse potential and the Debye model. The Born repulsion parameters of various compounds, which are necessary for determining the parameters of the Morse potential, have been determined empirically for elements belonging to every period of the periodic table. Using the parameters thus determined, the Debye temperature, the thermal expansion coefficient, and the Gruneisen constant of fluorite-type compounds have been calculated and then the isochoric and the isobaric heat capacities have been calculated over a wide range of temperatures. The calculated thermal expansion coefficients and isobaric heat capacities thus obtained are in good agreement with experimental values except for the anomalous temperature regions due to vacancy formation and phase transitions.     

Effect of Cristobalite and Quartz on the Properties of Gypsum Bonded Investment

Generally the gold investment material consists of cristobalite,quartz and plaster.The physical property of gold investment materials depends on its thermal expansion coefficients,compressive strength,and particles size distribution.Since the thermal expansion coefficient of cristobalite and quartz are 2.6×10^-6/℃and 2.32×10^-6/℃respectively,the composition ratio of each components influence the thermal and physical properties of gold investment materials.For the clinical applications,it is necessary to improve the properties of gold investment materials such as homogeneous size distribution and thermal expansion coefficients.In the present study,effect of inorganic fillers such as cristobalite and quartz on gold alloy investment was investigated to improve the properties of it.The compressive strength and thermal expansion coefficients of the specimens were evaluated.The results showed that cristobalite and quartz were homogeneously distributed by milling. The optimum compressive strength was obtained at the ratio of 42：22 cristobalite and quartz,respectively.     

Thermophysical properties of rubidium and lithium halides by γ-ray attenuation technique

The temperature dependence of linear attenuation coefficient, density and thermal expansion of rubidium halides (RbCl, RbBr and RbI) and lithium halides (LiCl, LiBr and LiF) has been studied by γ-ray attenuation technique. The γ-ray attenuation studies have been carried out using a γ-ray densitometer. The mass attenuation coefficients (μ _m ) of rubidium and lithium halides have been determined using γ-beam of different energies viz. (0.0595, 0.662, 1.173 and 1.332 MeV) respectively. The variation of density and coefficients of temperature dependence of density have been measured using Cs (0.662 MeV) source. The values of density at different temperatures have been used to estimate the values of linear attenuation coefficients (μ _l ) of the alkali halides studied in the present work for other γ-energies. The variation of thermal expansion of alkali halides studied in the present work has been compared with the results obtained from other methods. The variation in these thermophysical properties have been represented by linear equations. Volume thermal expansion coefficients and mass attenuation coefficients (μ _m ) of these compounds for the different energies have been reported and compared with data calculated by empirical and experimental method.     

Temperature coefficients of the electroelastic constants of quartz

In the domain between -40 degrees and 60 degrees C the temperature derivatives of the electroelastic constants of alpha-quartz are on the order of 10(-3) to 10(-4) N/(V-m- degrees C). This is about 100 times less than hitherto believed. The temperature coefficients T(e(ijk)) given in degrees C(-1 ) are on the same order of magnitude. Also contrary to earlier beliefs, available data cannot be used to determine all eight fundamental independent temperature coefficients T(e (ijk)) existing in the basic reference frame of quartz. Only six relevant quantities can be calculated, five of them as linear combinations of the fundamental T(e(ijk)). Their estimates, based on the available data, are given for 25 degrees C.     

Formation of β-FeSi2 thin films on non-silicon substrates

β-FeSi₂ films were prepared on non-silicon substrates by sputtering. The crystalline growth, stress induced cracks and adhesive ability to the substrate were investigated on substrate temperature and thermal expansion coefficient of substrate materials. It was found that crack formation in β-FeSi₂ films was dependent on the thermal expansion coefficients of CaF₂, MgO and quartz glass insulating materials. High-density cracks were observed from β-FeSi₂ films on CaF₂ and quartz glass substrates with large difference of the thermal expansion coefficient between β-FeSi₂ film and substrate materials, and it was crack-free on MgO substrate with a thermal expansion coefficient close to that of β-FeSi₂ films. Polycrystalline β-FeSi₂ films grew on Mo, Ta, W, Fe and stainless steel (SS) substrates at low substrate temperature around 400 °C. There was no α-FeSi₂ phase confirmed in the films. All the films had continuous structures without noticeable cracks even though they have different thermal expansion coefficients. Capacity-voltage measurements showed that β-FeSi₂ films formed on SS substrates has n-type conductivity, with residual carrier concentrations of about 1.3∼6.4 × 10¹⁸ cm^− 3. Auger electron spectroscopy depth profile measurements identified homogeneous distribution of Fe and Si atoms in the film region, but with a large interface region between the film and the substrate.     

Wide temperature-range Brillouin and Rayleigh optical-time-domain reflectometry in a dispersion-shifted fiber

The temperature dependences of spontaneous Brillouin and Rayleigh scattering intensities in a dispersion-shifted fiber have been measured over a wide temperature range by optical-time-domain reflectometry. It was found that spontaneous Brillouin and Rayleigh intensities normalized by room-temperature values have linear dependences on temperature, with coefficients (0.26 +/- 0.02)%/degrees C and (0.015 +/- 0.002)%/degrees C in temperature ranges -27-819 and 29-827 degrees C, respectively. Experimental results have demonstrated that both kinds of scattering can be used for distributed high-temperature measurement.     

Lam e-mode miniaturized quartz temperature sensors

Lam e-mode is very useful for realization of a miniaturized quartz crystal resonator because its resonant frequency principally depends only on the contour dimensions. Because the heat capacitance for the miniaturized quartz crystal resonator is small and the frequency response versus temperature is very rapid, the quartz crystal resonator is useful for application in temperature sensors. In addition, because a Lam e-mode quartz crystal resonator has zero temperature coefficients, designated LQ(1) cut and LQ(2) cut, and, particularly, the resonator for LQ(1) cut has a comparatively large value of the second-order temperature coefficient beta, a Lam e-mode quartz crystal resonator can be obtained with the large first-order temperature coefficient or when beta=0. In this paper, when cut angles phi=45 degrees and theta=45 degrees , alpha has a value of 44.6x10(-6)/ degrees C in the calculation and 39.9x10(-6)/ degrees C in the experiments with beta=0; when phi=51.5 degrees and theta=45 degrees , alpha=68.1x10(-6)/ degrees C in the calculation and 62.0x10(-6)/ degrees C in the experiments with a value of beta larger than that of phi=45 degrees and theta=45 degrees . For both cut angles, the calculated frequency change vs. temperature is found to be sufficiently large and slightly larger than the measured one.     

BAW temperature sensitivity and coupling in langanite

One of the new materials belonging to the trigonal class 32, to which quartz belongs, is langanite (LGN, La3Ga5.5Nb0.5O14). High-quality LGN single crystals are now available, and, although similar in composition and structure to langasite (LGS, La3Ga5SiO14), LGN has smaller thermal expansion coefficients and comparable piezoelectric constants to LGS. These are desirable material properties for both SAW and BAW applications that require low frequency dependence on temperature. This paper examines in detail the LGN characteristics: phase velocity, temperature coefficient of frequency (TCF), electromechanical coupling coefficient, and power flow angle for both singly and doubly rotated plate cuts. Contour plots of these characteristics are constructed, revealing orientation regions where zero TCF and high coupling exist and suggesting potentially interesting cuts for practical BAW device design. Temperature compensated cut regions with coupling coefficients as high as 0.16 are predicted, which is twice the value for AT-cut quartz, along with a temperature compensated cut with cubic behavior around room temperature for one of the sets of material constants used. With such desirable properties, LGN is a promising candidate material for BAW applications requiring low temperature sensitivity with superior bandwidth characteristics due to its values of coupling coefficient larger than quartz. Several other orientations with low TCF and high coupling are also identified.     

Temperature-insensitive fiber Bragg grating tilt sensor

A temperature-insensitive optical fiber tilt sensor is presented. The sensor scheme uses a prestrained fiber Bragg grating to sense the strain, which depends on the tilt angle. To compensate for the temperature effect, materials that have different linear thermal expansion behaviors are used for implementation of the sensor body. The differentiation in the linear thermal expansion would then cause a counter effect to the original temperature effect. Experimental tests show an accuracy of +/-0.167 degrees in tilt angle measurement. A temperature stability better than +/-0.33 degrees over the temperature range from 27 degrees C to 75 degrees C is demonstrated. The resolution 0.0067 degrees in tilt angle measurement is achieved by using our preliminary sensor with a dimension of 1 6 x 5 x 5 cm(3).     

Thermal Expansion of Ni–W,Ni–Cr,and Ni–Cr–W Alloys Between Room Temperature and 800 °C

The thermal expansion of Ni–W, Ni–Cr, and Ni–Cr–W alloys has been measured by quartz dilatometry for the 20 °C to 800 °C temperature range. It is found that substitution of nickel by tungsten leads to a considerable decrease of the thermal expansion coefficient (TEC), while chromium has only a small influence on the TEC of the alloy.     

Thermal expansion of beryllium oxide in the temperature interval 20–1550°C

The results of studies of thermal expansion of the sintered beryllium oxide in the temperature interval 20–1550°C are presented. Measurements were performed by a dilatometric method on a DIL-402C set-up manufactured by NETZSCH (Germany), with the accuracy of (1.5–2) × 10^?7 K^?1. Approximation dependences of coefficients of linear thermal expansion on temperature have been obtained and reference tables calculated. The data obtained are compared with data from the available literature.     

Thermal expansion of bismuth telluride

The results of X-ray and dilatometric measurements of the thermal expansion of bismuth telluride in the temperature range of 4.2–850 K have been critically analyzed. The joint statistical processing of the experimental data has been performed by the least squares method and the most reliable temperature dependences of the linear thermal expansion coefficients along the principal crystallographic axes α _a and α _c and the average linear coefficient [`(a)] _L\bar \alpha _L , as well as the density of Bi₂Te₃, have been recommended. The results indicate that the linear thermal expansion coefficients along the directions parallel and perpendicular to the cleavage planes decrease with an increase in the temperature in a narrow temperature range. At temperatures below 298 K, the character of the temperature dependences of the linear thermal expansion coefficients of Bi₂Te₃ has been analyzed in terms of the anharmonicity of the chemical bonding forces in the layer structure and anisotropy of the elastic constants. In terms of the deviations of the composition of the Bi₂Te₃ compound from the stoichiometric one and the real (defect) structure of the compound, a model has been proposed to explain the minimum in the (α _a T) dependence of Bi₂Te₃ near the melting temperature of bismuth. A method for calculating the temperature dependence of the linear thermal expansion coefficients of the anisotropic layer crystals using the data on the specific heat has been discussed, which provides good agreement of the calculated linear thermal expansion coefficients with the experimental data within the accuracy of the measurements of the linear thermal expansion coefficients.     

On the thermal expansion and crystallography of cubic (C) and monoclinic (B) forms of Gd2O3 in the temperature range 20 to 900°C

Thermal expansion coefficients of B-form (monoclinic) and C-form (cubic) Gd₂O₃ have been measured in the temperature range 20 to 900° C, by X-ray diffractometry. The thermal expansion coefficients of both cubic and monoclinic material are linear in the temperature range studied. The expansion of monoclinic material is, however, very anisotropic, and the minor axis of the thermal expansion ellipsoid is not parallel to the edge of the primitive cell to which Gd₂O₃ has been assigned. It is noted that the anisotropy in expansion behaviour of this material indicates that anisotropic growth probably occurs during irradiation.     

Negative temperature coefficient of single-walled carbon nanotube-gold nanoparticle hybrid structures

Single-walled carbon nanotubes (SWNTs) were grown on gold nanoparticle (GNP) coated quartz substrates by alcohol catalytic chemical vapor deposition. The GNP coated substrates were coated with Co catalyst by a dip-coat method. The growth was then carried out at 800 degrees C under a pressure of 10 Torr in an atmosphere of ethanol vapor for 30 min. Characterizations have shown larger SWNT diameters with higher negative temperature coefficients for GNP coated substrates as compared to those of quartz substrates without GNPs. It is attributed that SWNT-GNP hybrid structures have a higher fraction of semiconductor-type pathways.     

Micromachined resonant temperature sensors: theoretical and experimental results

Describes the study of quartz temperature sensors based on new bulk acoustic wave microresonators operating in thickness modes. First, we compare the thermal sensitivity and the electromechanical coupling coefficients of singly or doubly rotated cuts. These investigations allow us to select some cuts with both a good thermal sensitivity and piezoelectric characteristics. In the second part, emphasis is placed on the micromachining of resonators suspended by four bridges. These two theoretical considerations lead to the choice of three cuts. Experimental measurements are then presented. The temperature-frequency characteristics of the resonators are measured over the range 20 to 100 degrees C. Motional resistances and Q factors are determined at room temperature.     

Development of a Laser Interferometric Dilatometer for Measurements of Thermal Expansion of Solids in the Temperature Range 300 to 1300 K

A laser interferometric dilatometer has been developed for measuring linear thermal expansion coefficients of reference materials for thermal expansion in the temperature range 300 to 1300 K. The dilatometer is based on an optical heterodyne interferometer capable of measuring length change with an uncertainty of 0.6 nm. Linear thermal expansion coefficients of silicon were measured in the temperature range 700 to 1100 K. The performance of the present dilatometer was tested by a comparison between the present data and the data measured with the previous version of the present dilatometer and the data recommended by the Committee on Data for Science and Technology (CODATA). The present data agree well with the recommended values over all the temperature range measured. On the other hand, the present values at lower temperatures are in poor agreement with the previous experimental data. The combined standard uncertainty in the present value at 900 K is estimated to be 1.1×10^–8 K^–1.