Аннотация:Titanium and niobium atoms are distinctive with high electronic polarizabilities thus being indispensable for pronounced optical non-linearity (ONL) in many families of ferroelectrics and optical materials. In the KTiOPO4 (KTP) family Nb-doping is strongly restricted and known to be only partial. We have carried out comparative investigation of niobium ions and similar to them by size and charge antimony ions on structure, ionic conductivity, ferroelectric properties and non-linearity in the KTP-like regions of solid solutions: K1-xTi1-xNbxOPO4 (1), K1-xTi1-xSbxOPO4 (2), KSb1-xNbxOGeO4 (1), KTa1-xNbxOPO4 (4), and KTi1-xNbxOP1-xGexO4 (5). Single crystals of (1) and (2) up to x~0.15 Have been obtained by crystallization of fluxes while solid-state reactions have been employed to produce single-phase powders of (3)-(5). Here the region of solid solutions with a KTP structure are extended to x= 0.75 (3), ≈ 0.75 (4), ≈ 0.85 (5). According to our SHG data substitution of Nb5+ into systems (1) and (2) lowers the Tc and reduce their ONL. Ferroelectric phases transitions smears and disappears in potassium-deficient solid solutions. Temperature investigation of powder neutron diffraction for (1) and (2) reveals potassium atom deficiency more than required by Nb5+ or Sb5+ charge compensation, especially above Tc. Some additional (interstitial) positions are supposed for K+ playing the key role in both dielectric relaxation and ionic conductivity enhancement. Typical relaxor behavior is found for the first time in the KTP-based compositions. Substitution of Nb5+ into system (3) and (4) raises Tc and increases ONL to values close to that for pure KTP. In (5) initial drop of ONL is changed by growing as the composition becomes closer to KNbOGeO4.
