Growth and Neutron Diffraction Investigation of Ca3NbGa3Si2O14 and La3Ga5.5Nb0.5O14 Crystals

Abstract EN

Langanite (La3Ga5.5Nb0.5O14, growth atmosphere: 99% Ar + 1% O2) and kanigasite (Ca3NbGa3Si2O14, growth atmosphere: 100% Ar) crystals grown by the Czochralski technique in Ir crucibles along <0001> direction have been firstly investigated by neutron diffraction.

The difference between the compositions of upper (La2.935(2)□0.065)(Ga0.450Nb0.550(3))Ga3(Ga1.965(4)□0.035)(O13.90(1)□0.10) and lower (La2.940(1)□0.060)(Ga0.590Nb0.410(2))Ga5(O13.82(1)□0.18) parts of orange langanite crystal was found.

It was established that the colorless Ca3NbGa3Si2O14 crystal grown by using the single-crystal charge has the composition (Ca2.95□0.05(1))NbGa3Si2O14 and is less defective in comparison to the yellow one grown by using the charge prepared by conventional solid-state reaction.

For Ca3NbGa3Si2O14 and La3Ga5.5Nb0.5O14 crystals the possibility of microtwin formation (two unit cells connected by the translation: 1/2 z) was revealed for the first time.

It was found that the difference between the color of crystals is attributed to the qualitative differentiation of oxygen vacancies.