Nonclassical nonlinearity and crystal defects in lithium niobate

• Published in: The Journal of the Acoustical Society of America 2016-10, Vol.140 (4), p.3324-3325
• Main Authors: Chatterjee, Chandrima, Cremaldi, Lucien, Ostrovskii, Igor
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4970590

Nonclassical nonlinearity (NN) in ultrasound attenuation and acoustic memory in LiNbO3.may be connected to crystal defects. The optical spectra of photoluminescence (PL) and absorption taken from 350—900 nm reveal multiple point defects and impurities such as F-center, NbLi +, Fe, Ba, Ar, Xe and others. The spectra are taken at room temperature from the Czochralski grown bulk crystals and wafers. The samples are scanned by taking PL spectra from different locations along the z- and y-axes. The data from several samples reveal a nonuniform distribution of the defects along the crystallographic axes. The dependencies of PL peaks versus position have a sine-like component on top of some constant intensity. For instance, a scan for F-center has a period (P) from 0.27 to 0.75 mm and for Ba impurity from 0.25 to 0.75 mm in bulk crystals. In the wafers, P may be smaller, that is 0.1 mm and smaller. However, a ratio of maxima to minima in PL peaks is higher for bigger P. The overall spread of P is roughly from < 0.1 mm to about 1 mm. Some defects are electrically charged, and may influence the piezoelectric properties. Consequently, a real crystal has some constants which are nonuniform along its axes. The measured periods P correspond to ultrasonic wavelengths in the Megahertz frequency range. The comparison of the periods P in defects distributions with the frequencies of NN phenomena points to considering crystalline defects as those responsible for the NN observed in LiNbO3.