David K. T. Chu

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/sub 4/ (RTP) and RbTiOAsO/sub 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/sub 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 /sub c33/ for hydrothermally grown KTP) that makes it attractive for many piezoelectric applications.<<ETX>>

Curie temperatures and dielectric properties of doped and undoped KTiOPO/sub 4/ and isomorphs

The Curie temperatures and dielectric properties of KTiOPO/sub 4/ (KTP), RbTiOPO/sub 4/, KTiOAsO/sub 4/, RbTiOAsO/sub 4/, CsTiOAsO/sub 4/, Ba:KTP, and Ga:KTP were measured with small-signal relative dielectric permittivity ( kappa ) analysis, piezoelectric resonance analysis, and optical second harmonic generation. All the isomorphs and the doped KTP exhibit lower Curie temperatures than KTP, ranging from 637 degrees C for CsTiOAsO/sub 4/ to 955 degrees C for hydrothermally (HT) grown KTP. The Curie-Weiss law is obeyed in all samples. With the exception of CsTiOAsO/sub 4/, all doped and undoped crystals show large dielectric relaxation at frequencies below 100 KHz throughout the temperature range of 500 degrees C-800 degrees C. For the barium-doped KTP, it was found that the Curie temperature decreases with increasing Ba/sup ++/-doping concentration. Barium doping also significantly modifies dielectric and piezoelectric properties of KTP.<<ETX>>

Ferroelectric phase transition in KTiOPO4: An optical second‐harmonic generation study

The ferroelectric phase transition in a single‐domain KTiOPO4 (KTP) crystal is studied with optical second‐harmonic generation. The optical nonlinearity decreases continuously with increasing temperature and vanishes at the Curie point (TC=952 °C) and above. Over a broad temperature range in the ferroelectric phase, the nonlinear optical coefficient d33∝(TC−T)0.5. This behavior is in good agreement with the Landau theory for second‐order ferroelectric phase transitions.

Acoustic and optical properties of thallium ion‐exchanged KTiOPO4

Both acoustic and optical properties of thallium ion‐exchanged KTiOPO4 (Tl:KTP) plates were examined. Surface acoustic wave (SAW) velocity of the thallium‐exchanged z‐cut KTP possesses a reduction of 13% from the unchanged KTP. Temperature stability of SAW resonance (1/f0 df/dT) changed from ≊−81 ppm of an untreated z‐cut KTP substrate to ≊−121 ppm of a z‐cut Tl:KTP substrate. Large optical refractive indices changes at the Tl ion‐exchanged surface were observed [Δneff(TE)≊0.3, Δneff(TM)≊0.22]. Tl ion concentration profile from the crystal surface into substrate was also studied using electron beam microscopy and the optical index m‐line measurement. Tl‐exchanged KTP, therefore, possesses both acoustic and optical waveguiding properties.