Evaluation of Material Constants and Temperature Properties in Lanthanum Calcium Oxoborate LaCa 4 O(BO 3 ) 3 Single Crystals Hiroyuki SHIMIZU  , Kaoru KODAMA, Hiroaki TAKEDA, Takashi NISHIDA, Takashi SHIKIDA 1 , Soichiro OKAMURA and Tadashi SHIOSAKI Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan 1 Research Development Division, Sakai Chemical Industry Co., Ltd., 5-1 Ebisujima-cho, Sakai, Osaka 590-0985, Japan (Received June 7, 2004; accepted July 12, 2004; published September 22, 2004) Lanthanum calcium oxoborate LaCa 4 O(BO 3 ) 3 (LaCOB) single crystals were successfully grown by the Czochralski technique. It was found that LaCOB crystals belong to the monoclinic system (point group m) and the total number of independent material constants that should be determined is 27. Twenty-four of the 27 material constants at room temperature were determined by the resonance-antiresonance method. The normalized first-order temperature coefficients of some constants e.g., " 11 T , " 22 T , " 33 T and " 13 T determined at 10 kHz were 56.30, 273:6, 135.8 and 258:4 and d 11 and d 12 were 408:3 and 83.60 ppm/  C, respectively. Additionally, the thermal expansion coefficients e.g.,  11 ,  22 and  33 determined on a single crystal cut along the X, Y and Z rectangular directions by the thermodilatometry measurement were 7:36  10 6 , 8:17  10 6 and 11:4  10 6 /  C, respectively. As a result of the evaluation, most of the material constants and temperature properties necessary for investigating the properties of piezoelectric devices typified by SAW were obtained. [DOI: 10.1143/JJAP.43.6716] KEYWORDS: single crystal, material constants, temperature coefficients, linear thermal expansion coefficients 1. Introduction At present, new piezoelectric materials that have large electromechanical coupling factors and small temperature coefficients of delay, have been required with the progress in the electronics field. Surface acoustic wave (SAW) devices such as frequency filters, resonators and oscillators are widely used. The characteristics of SAW devices depend on the type of piezoelectric materials used. Thus, it is important to find a crystal substrate with good propagation character- istics. Recently, rare-earth calcium oxoborate, RCa 4 O(BO 3 ) 3 (R ¼ La-Lu, Y; abbreviated REECOB), single crystals have been developed; they exhibit excellent nonlinear optical properties and can be grown by the Czochralski (Cz) technique at a low cost. 1–4) The optical applications of wavelength converters to second- and third-harmonic gen- eration have been actively investigated. Since REECOB belongs to the monoclinic system (point group m), and its single crystals have piezoelectricity, we have paid attention to REECOB as new piezoelectric material for SAW devices. The piezoelectric properties of YCOB and GdCOB single crystals have been reported. 5,6) The material constants of GdCOB crystals have been determined by Wang et al. 7) Although, there is a report concerning the optical properties of LaCOB single crystals, there are as yet no reports on their piezoelectric properties. Thus, we have paid attention to the piezoelectricity of LaCOB single crystals with lower melting points in the REECOB series and characterized SAW and pseudo-SAW (PSAW) properties on the X-, Y - and Z -cut substrates. 8) This led to the expectation that the LaCOB crystal will become performance-competitive with existing Li 2 B 4 O 7 and La 3 Ga 5 SiO 14 crystals. It is important to simulate SAW properties theoretically for which accurate material constants including temperature coefficients are necessary. Mason has reported a measurement method for material constants of point group 2, 9) however, very few numerous experimental and theoretical works concerning the material constant of point group m have been reported. In this study, we describe the material constants and temperature coefficients of LaCOB single crystal prepared successfully by the Cz technique. The linear thermal expansion coefficients of these crystals were also deter- mined. 2. Experimental 2.1 Crystal growth and characterization Single crystals were grown by a conventional RF-heating Cz technique using an iridium crucible. The starting materials were prepared by mixing 99.99% purity La 2 O 3 , CaCO 3 and B 2 O 3 powders in a stoichiometric ratio while taking ignition loss into consideration. The powders were mixed in air, and then calcined at 1000  C for 2 h. The calcined powders were heated at 1200  C for 2 h. The resulting LaCOB powders were pressed uniaxially and charged into the crucible. The growth was carried out at an Ar gas flow rate of 1.8 L/min. The pulling and rotation rates were 2.0–3.0 mm/h and 20 rpm, respectively. As- grown crystals were postannealed at 1000  C for 10 h in air. For the first growth experiment, a h010i GdCOB crystal was used as a seed. The growth direction of the obtained crystal was confirmed to be h010i by a backscattering Laue X-ray technique. For further experiments, seed crystals were prepared by cutting this crystal. The phase identification of grown crystals was performed by powder X-ray diffraction (XRD) analysis. The chemical composition of the crystals was determined by inductively coupled plasma emission spectrometry (ICP-ES). 2.2 Thermal expansion coefficient measurement Thermal expansion coefficient (TEC) was measured to investigate the thermal expansion anisotropy of LaCOB single crystals. There are three independent expansion components  11 ,  22 and  33 along the rectangular X-, Y - and Z -axes, respectively. Measurements were carried out using a dilatometer (TD5000S: MAC science) in the  E-mail address: s-hiroyu@ms.naist.jp Japanese Journal of Applied Physics Vol. 43, No. 9B, 2004, pp. 6716–6720 #2004 The Japan Society of Applied Physics 6716