Non-linear optical single crystals of barium mixed calcium tartrate tetrahydrate with molecular formula Ca0.8Ba0.2C4H4O6.4H(2)O (CBT) have been grown in gels using a chemical reaction method at ambient temperature. The physical and chemical characteristics of gel grown CBT crystals have been investigated by employing Vickers micro hardness, etching, and thermal techniques. The single crystalline habit of CBT is deviated from that of calcium tartrate tetrahydrate crystals. Because of lower dehydration coefficient Ba2+ is strongly incorporated in calcium tartrate tetra hydrate (CTT) crystal lattice. The etch pit density is greater in CBT than in pure CTT crystals due to lattice distortion. The mechanical strength of the pure CTT is increased by doping it with 20% barium. The two dimensional diffusion mechanism is suggested for the solid state non isothermal dehydration step in CBT crystals. The CBT crystals turn out to be tetrahydrate and crystals are found to be thermally less stable than pure crystals. (C) 2002 Elsevier Science B.V. All rights reserved.