The second harmonics generation of Nd-laser radiation (A = 1.06 microns) of the isomorphic family of crystals with yttrium-aluminium borate (YAB) structure -RAI, (BO,), (R = Y, Sm, Eu, Gd, Dy, Er, Ho, Tu) -investigated using the powdor method and the theoretical calculation of SHG-coefficients -are reported. The rcfraction indices (for I = 5481 A) and optical sign for all studied YAB-typo crystals are determined with the help of the immersion method. All studied crystals possess PM direction and oee-interaction. The SH-intensity is of KDP order of magnitude, with reasonable correlation of experimental and theoretical data. Theoretical analysis of the contributions of different ions t o the integral d;: magnitude has shown identical signs for all ion species in YAB structure type.Es wird uber die Erzeugung der zweiten Harmonisehen dcr Nd-Laser-Strahlung (1, = 1,06 pm) der isomorphen Kristallreihe mit Yttrium-Aluminium-Borat-Struktur -RAl,(BO,), (R = Y, Sm, Eu, Gd, Dy, Er, Ho, Tu) -die nach der Pulvermethode und mit Hilfe der theoretisohen Berechnung der Koeffizienten der 2. Harmonischen untersucht wurden, berichtet. It was reported by BALLMAN (1962a) on flux growing and preliminary investigations of some crystals with yttrium-aluminium borate (YAB) structure -RA13(B03)4 whereR = Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb. The structure of this isomorphic family is similar to the structure of the carbonate mineral huntite (CaMg,(CO,),). From the whole group more details are known for the YALJBO,),: space group R 32; cell parameters: a = 9.287 A, C = 7.256 A ; optically negative; no = 1.775, n, = 1.715; density 3.70 g c 1 r 3 ; Mohs hardness 7.5. All investigated crystals showed piezoelectric activity (BALL-MANN 1962b), and it was predicted by REZ the possibility of considerable optical nonlinearity. Now we report on the investigation of second harmonics generation (SHG) of Nd-laser radiation, fulfilled on powders and tiny crystals and theoretical calculation of SHG-coefficients.Tiny crystals of the studied family were grown in the flux in the temperature range 1150-850 "C with potassium trirnolybdate as solvent (LEONYUK et al.)

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Solution-melts based on PbF,-B,O, and Bi,O,-B,O, were used in studying the stability regions and for growth, by way of spontaneous crystallization, of crystals up to 3 iiim in size of twelve cornpounds having the general formula RGI+@&),. All of these compounds are isostructural with carbonate mineral huntite. Their composition is highly dependent on that of the crystallization medium. The facing of the crystals is characterized by a small number of simple forms {lOII}, {1120}, (2IIO}, and less frequently {0221}, { 01 12}, { 40;11}. The examined parameters include the IR spectra, luminescence spectra, heat of formation from oxides, harness (6 to 8 units on the Mohs scale) and others.

Crystals of Rare-earth-ferrous BoratesCrystals of rare-earth-ferrous borates (structure of carbonate mineral huntite, space group I3 32) were obtained from the solution-melt with the Bi203-B203 base. It was established by the methods of X-ray structural and chemical analyses that large amounts of Bi from the solution became part of the crystals affecting their solubility, morphology and hardness. Solubility curves for YFe-, NdFe-, and ErFe-borates in the 3 B&03 . 5 B,O, melt were plotted. Refinement of crystalline structure of NdFe-borate showed that bismuth takes up place of rare-earth ion in the crystal lattice. Parameters of unit cells, density and refractive indexes of t,he obtained crystals were measured. Rare-earth-ferrous borates belong to the large group of isostructural compounds with the general formula of RM,(BO,),, where R is Ln, M denotes Al, Pe, Ga, Cr. All of them are isostructural to huntite (space group R 32). These crystals are piezoelectric substances, they possess non-linear and laser properties, very hard, refractory and resistent to acids and alkali. Rare-earth-ferrous borates, with the exceptionof Ce, Pr, Yb and Lu were synthetized by the method of solid-phase reactions (with 10% excess of H,BO,) by JOUBERT in the sealed gold ampoule (JOUBERT et al.). Fine crystalls (0.5 x 0.5 x 1.0 mm) of GdPe-and YPe-borates were also obtained as a result of spontaneous crystallization by TAKAHASHI from solution in the Bi,O,-B,O, and PbF,-B,O, melts (TAKAHASHI et al.). Detailed study of RFe,(BO,), was not carried out for lack of high quality single crystals.Due to incongruent melting of RFe,(BO,), the authors studied conditions of their crystallisation from solution-melts of molybdates and vanadates of alkali elements