Ca2.90Li0.30Nb1.93Ga2.76O12 and La0.57Ca2.38Li0.72Nb2.01Ga2.26O12 crystals: New substrates with more perfect lattice constant for garnet-type film

• New substrate crystals of CLNGG and LCLNGG were successfully grown by Czochralski method.
• Lattice-mismatch and Ga2O3 volatilization are major inducements of crack and inclusion defects.
• LCLNGG crystal has a more perfect structure by doping Li+, Nb5+, and La3+ ions.
• LCLNGG crystals may be a better candidate substrates for highly Bi or Ce doped-YIG film.

Two new substrate crystals, Ca2.90Li0.30Nb1.93Ga2.76O12 (CLNGG) and La0.57Ca2.38Li0.72Nb2.01Ga2.26O12 (LCLNGG), were successfully grown by the Czochralski method. Compared with Gd3Ga5O12 crystal, CLNGG and LCLNGG crystals possess the lattice constants better matched with those of highly Bi- or Ce-doped YIG films that have been widely used in the magneto-optical devices. The high quality and performance films are expected to be obtained by using CLNGG or LCLNGG as substrate material. In this paper, the structures of CLNGG and LCLNGG are refined by the Rietveld method, and the influences of doping on the crystal structure, transmittance, electrical conductivity, thermal expansion coefficient are discussed. Then, the causes of crystal defects are analyzed in detail. The results show that the lattice-matched seed and the atmosphere containing suitable oxygen partial pressure are crucial to obtain high-quality CLNGG crystal without crack and inclusion defects. Since the oxygen-vacancy defects are effectively reduced by doping Li+, Nb5+, and La3+ ions, LCLNGG crystal has a more perfect crystal structure, fewer vacancy defects and dislocation defects than CLNGG crystal.