Crystal growth and morphology of hydrothermally grown lithium borates
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R. Rodriguez-Clemente Institute of Materials Science of Barcelona, CSIC Campus UA.B.E.-08193, Cerdanyola, Spain (Received 24 November 1992; accepted 25 February 1993)
The Li 2 O-B 2 O 3 -H 2 O system has been studied under hydrothermal conditions. Li4B7O12Cl, Li 2 B 4 O 7 , Li 3 B 5 O 8 (OH) 2 , Li 2 HBO 3 , and LiH 2 B 5 O 9 are the phases crystallizing in this system at 250 °C and P < 100 bars. The growth of these phases has been discussed in brief. Also, the growth morphology of these phases has been studied with reference to the growth parameters.
I. INTRODUCTION Alkali borates have been studied for the past seven decades. Over 85 phases have been established with 58 known compounds belonging to over eight different structure types. The study of borates in general was purely of academic interest and did not carry any great significance until the late 1970s when mixed alkali borates were first used in miniature laser applications.1 Subsequently, lithium boracite was reported to be exhibiting superionic properties.2 However, these applications did not generate any special interest among materials scientists, but it is the /3-barium borate3 which opened a new chapter for borates. Further, the recent discovery of piezoelectric Li2B4O7 (Ref. 4) and nonlinear optical LiB 3 O 5 (Ref. 5) has attracted a great deal of attention from materials scientists, and today it is the alkali borates that are being studied extensively worldwide. The growth of alkali borates is being carried out mostly by melt and flux techniques. There are some reports about the solid-state reactions, but the work on borates in general by hydrothermal technique was almost untouched except for the past decade. Only a few alkali borates have been obtained by the hydrothermal technique. The Li 2 O-B 2 O 3 system was first studied in 1958 by Sastry and Hummel by the flux method, but the study of pure alkali borate systems under hydrothermal conditions was realized only in recent years.6 Several new phases have also been reported under hydrothermal conditions. The present authors have studied the Li 2 O-B 2 O 3 -H 2 O system under lower PT conditions (T = 250 °C, P ~ 100 bars) using the hydrothermal technique. The experiments with varying PT conditions are in progress. Till the 1980s, work on borates was mainly academic except for the mixed alkali rare earth borates and lithium boracite crystals. Subsequently, the trend shifted toward the J. Mater. Res., Vol. 8, No. 9, Sep 1993
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growth of various alkali borates and their applications. Although its analogous compounds, such as phosphates and silicates, were studied essentially with reference to their morphology for the past 70 years, the morphology of borates has not been studied in spite of their great technological importance. There are only a very few reports in the literature dealing with the morphology of alkali borates. Hence, the present authors have made an attempt to study the morphology of hydrothermally grown lithium borates systematica
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