Beam-focused SH wave transducer based on YSr_(3)(PO_(4))_(3)piezoelectric crystal for high temperature structural health monitoring

Guided-wave-based structural health monitoring(SHM)technology is of great importance for real-time inspection of high-temperature structures.The fundamental shear horizontal(SH_(0))wave is believed to be an ideal wave mode for developing SHM systems due to its nondispersive characteristics.However,currently very limited SH_(0)wave transducers can be used for SHM of high-temperature structures due to the limitation of materials.Herein,a novel YSr_(3)(PO_(4))_(3)(YSP)piezoelectric crystal in the space group I43d was grown.Experiments show that the face-shear piezoelectric coefficient d_(14)(d_(14)=d_(25)=d_(36))is 9.7 pC/N and varies little from 25 to 800℃.Then a beam-focused SH_(0)wave piezoelectric transducer is developed based on face-shear-mode YSP wafers.Both finite element simulations and experimental results indicate that the YSP-based transducer can excite pure SH_(0)wave and focus the wave energy along two opposite main directions.Especially,the obtained SH_(0)wave beam is highly concentrated with a small divergence angle of less than 30°,originating from the high working frequency range from 300 to 400 kHz.The excellent temperature stability of the as-grown YSP crystal makes the proposed SH_(0)wave piezoelectric transducer very suitable for SHM of high-temperature structures.

Nd-doped structurally disordered YSr_(3)(PO_(4))_(3) single crystal:Growth and laser performances

Disordered-structure crystals have drawn increasing attention as promising ultrashort laser material hosts owing to their broad linewidth.Herein,a novel disordered Nd:YSr_(3)(PO_(4))_(3)(Nd:YSP)crystal with good quality was successfully grown via the Czochralski pulling technique.The absorption and fluorescence spectra of the Nd:YSP single crystal were recorded at ambient temperature.The maximum absorption cross section for Nd:YSP single crystal is found to be approximately 3.89×10^(-20) cm^(2).The stimulated emission cross section for Nd:YSP crystal at~1060 nm was determined to be 7.64×10^(20) cm^(2) with the full width half maximum value of 22 nm.The fluorescence lifetime of the Nd3+ions in the Nd:YSP crystal is fitted to be 288μs.Diode-pumped continuous-wave laser operation is firstly realized at approximately 1060 nm.The maximum output power value from the Nd:YSP crystal is 714 mW,corresponding to a slope efficiency of-12.8%.The results indicate that the Nd:YSP crystal with a disordered structure may be a promising disordered laser host.

The electromechanical features of LiNbO_(3) crystal for potential high temperature piezoelectric applications

Lithium niobate(LiNbO_(3),LN)crystal is a multi-functional material with favorable piezoelectric,nonlinear optical and electro-optic properties.In this study,the electromechanical properties of the radial extensional(RE)and the thickness extensional(TE)modes of the congruent LN are studied and the temperature dependent behaviors are revealed.The RE mode electromechanical coupling factors(kp)for the Y-and Z-oriented discs are calculated and found to be 3.8%and 24.7%,respectively,which are nearly the same as the experimental results of 3.8%and 25.2%,respectively.The maximum RE and thickness shear(TS)modes electromechanical coupling factors are obtained to be 47.6%and 68.5%for the Yx/25
and Yx/167
crystal cuts,respectively.The LN crystal possesses good temperature stability of the electromechanical coupling factors(RE and TE modes)from 20℃ to 500℃,where the variations of kp and kt for the Y-oriented discs are<8.0%and<1.8%,respectively.

Electrical properties of yttrium calcium oxyborate crystal annealed at high temperature and low oxygen partial pressure

The yttrium calcium oxyborate crystal(YCa_(4)O(BO_(3))_(3),YCOB)has been actively studied for hightemperature piezoelectric sensing applications.In this work,the stability of electric properties of YCOB crystal annealed in critical conditions(high-temperatures of 900-1100℃ with a low oxygen partial pressure of 4×10^(-6) atm for 24 h)was investigated and the recovery mechanism for the electrical resisitivity,dielectric permittivity and dielectric loss were studied,taking advantage of the X-ray photoelectron spectra and the first principle calculations.The electrical resistivity of the annealed YCOB crystal was slightly decreased when compared to the pristine counterpart,being(2-5)×10^(7) Ω·cm at 850
C.The dielectric permittivity and dielectric loss were found to increase after annealing,showing recoverable behaviours after thermal treatment above 650℃ in air.The calculated vacancy formation energy indicates that the oxygen vacancy is the dominant defects in YCOB.The formation of oxygen vacancy weakens the chemical bonding strength between B(Ca or Y)and O atoms,introduces extra donor levels in the band gap,which excites the electrons to conduction band more easily thus enhances the electrical conductivity and dielectric loss.The recovered electrical properties are believed to be associated with the reduced vacancy defects at elevated temperatures in air.

Electro-elastic features of YBa3(PO_(4))3 and YbBa3(PO_(4))3 crystals with pure face-shear mode for acoustic wave sensor applications

The fundamental shear horizontal(SH0)waves have been proved to be a very useful method for nondestructive testing due to their non-dispersive characteristics.Currently,although several methods have been proposed to generate SH0 waves,it is still a challenge to obtain pure SH0 wave mode efficiently.Herein,in this study,non-centrosymmetric YBa3(PO_(4))3(YBP)and YbBa3(PO_(4))3(YbBP)crystals with pure face-shear mode were grown via the traditional Czochralski pulling method at temperatures above 1800℃.High resolution X-ray diffraction was carried out to evaluate the crystalline quality.Results showed that the YBP and YbBP crystals were of good quality,with the full width at half-maxima being on the order of 42.500 and 52.300,respectively.Moreover,the full set of electro-elastic constants for the YBP and YbBP crystals were determined and collated using a combination of impedance and pulse-echo methods.The piezoelectric coefficient(d14)of the YBP and YbBP crystals were determined to be 10.6 pC/N and 11.4 pC/N,respectively,corresponding to the electromechanical coupling coefficient(k14)equal to 15.4%and 15.9%,exhibiting large and pure face-shear vibration mode.Collectively,these results indicate that the YBP and YbBP crystals are promising for acoustic wave sensing application.

Passively Q-switched self-frequency doubling Nd3+:ReCa4O（BO3）3（Re=Y,Gd） lasers with tin diselenide as a saturable absorber

With tin diselenide(SnSe2)film as a saturable absorber(SA),the passively Q-switched self-frequency doubling(SFD)lasers were realized in Nd^3+:ReCa4O(BO3)3(Re=Y,Gd)crystals.For Nd:YCa4O(BO3)3 crystal,the maximum average output power at 532 nm was 19.6 mW,and the corresponding pulse repetition frequency,pulse duration,single pulse energy,and peak power were 17.6 kHz,91.9 ns,1.1μJ,and 12.1 W,respectively.For Nd:GdCa4 O(BO3)3 crystal,these values were 14.5 mW,22.1 kHz,48.7 ns,0.66μJ,and 13.5 W.

Temperature dependent behaviors of electro-elastic properties of NdCa_(4)O(BO_(3))_(3)crystal with monoclinic symmetry

Rare-earth calcium oxyborate crystals(RECa_(4)O(BO_(3))_(3),RECOB,RE:rare-earth elements)are a kind of multifunctional crystal materials.In this work,the temperature dependent behaviors of the electroelastic constants of NdCOB crystal were investigated over the temperature range of-80-200℃,and their temperature coefficients were evaluated.It is found that NdCOB crystal possesses minimal variation of relative dielectric permittivities(<3%).The temperature coefficient of frequency for ZY cut with width shear vibration mode is in the order of 0.07×10^(-4)/℃.The temperature coefficients of the elastic compliances are obtained to be in the range of-33.0×10^(-4)/℃-32.2×10^(-4)/℃.Particularly,the sand swere found to show low temperature coefficients of the elastic compliances,i.e.1.0×10^(-4)/℃and-0.4×10^(-4)/℃,respectively,indicating the existence of zero temperature coefficient of frequency crystal cut.Furthermore,the electromechanical coupling factors and piezoelectric coefficients as a function of temperature were studied.The electromechanical coupling factor kand piezoelectric coefficient dare determined to be~30.8%and~15.2 pC/N at room temperature,respectively.The large piezoelectric response and zero temperature coefficient of frequency indicate the potential usage of NdCOB crystal for piezoelectric frequency devices over a wide temperature range.