D.F. O'Kane

The tungsten bronze field in the system K2O|Li2O|Nb2O5

A limited portion of the liquidus field and the entire subsolidus stability region has been determined for tungsten bronze-type solid solutions in the K2O|Li2O|Nb2O5 system. The tungsten bronze phase does not occur with completely filled alkali cation sites at the composition K3Li2Nb5O15, but exists exclusively in the high niobia region above the KNbO3|LiNbO3 pseudojoin. Equilibrium relationships defining conditions for the growth of electrooptic crystals, and dielectric, optical, and x-ray measurements establishing the influence of composition on structure and properties are presented and discussed.

Phase equilibria in the NaNbO3BaNb2O6 system

Abstract Complete liquidus and solidus equilibria have been established by DTA and quench techniques in the system NaNbO 3 BaNb 2 O 6 , which contains the pseudo-tetragonal bronze NaBa 2 Nb 5 O 15 . While little solid solution occurs in the end member compounds, the tungsten bronze phase shows extensive solid solubility from 62 to 83 mole % BaNb 2 O 6 . These results and subsolidus DTA and dielectric measurements are discussed in relation to the crystal chemistry of the bronze structure. The essential features of the phase diagram have been confirmed by Czochralski crystal growth experiments at selected melt compositions in the bronze(ss) field.

FERROELECTRIC AND OPTICAL PROPERTIES OF KSr2Nb5O15

A new transparent tetragonal crystal, KSr2Nb5O15, of the tungsten bronze type has been found to be ferroelectric with a Curie temperature of ≈160°C. At room temperature the electro‐optic coefficient, r∥, is 1.3 × 10−8 cm/V and e∥ is approximately 1,000.

Raman measurements of NaBa2Nb5O15 and related ferroelectrics

Abstract We report results of Raman measurements of several tungsten-bronze type ferroelectrics. The results for vibrations that have a polarization along the ferroelectric axis are largely determined by the NbO6 octahedra and are similar to the perovskites.

Alkali-rare earth niobates with the tungsten bronze-type structure

Abstract A new series of alkali-rare earth niobates of the type A 2 + RE 3+ Nb 5 O 15 is described. These materials are solid solutions with a tetragonal bronze-like structure, and exhibit dielectric anomalies from −120°C to +300°C. The dielectric properties of these phases are examined in terms of the crystal chemistry of the tetragonal bronze-type structure.

Infrared TV system of computer controlled Czochralski crystal growth

Abstract An infrared television system of computer controlled Czochralski crystal growth is described. Crystal diameter measurements were made by computer analyses of the TV data, and the power to the crystal puller was controlled by the computer to regulate the diameter. Single crystals of (KNbO3)10(LiNbO3)35(BaNb2O)55 were grown near 1400°C. Relative temperatures on the melt surface and growing crystal were obtained from the TV data.

Tungsten bronze-type crystals grown in molten solutions of the pseudosystem KNbO3LiNbO3BaNb2O6

Abstract Electrooptic single crystals having a room temperature tetragonal tungsten bronze-type structure were grown from the pseudosystem KNbO 3 LiNbO 3 BaNb 2 O 6 using covered platinum crucibles cooled at 2°C/hr. The largest and best quality crystals were grown from molten solutions with compositions approximately between K 3 Li 2 Nb 5 O 15 and KBa 2 Nb 5 O 15 . The K 3 Li 2 Nb 5 O 15 functions as a flux and the compositions of the grown crystals lie close to KBa 2 Nb 5 O 15 . These tungsten bronze-type crystals, which can be represented as KBa 2 Nb 5 O 15 solid solutions with LiNbO 3 and K 3 Li 2 Nb 5 O 15 , are not microtwinned and a large range of the bronze compositions phase match the Nd:YAG laser (1.06 μ) for second harmonic (0.53 μ) generation without double refraction above room temperature.

Optical and Ferroelectric Properties of KxNa1−xBa2Nb5O15

The ferroelectric tungsten—bronze system KxNa1−xBa2Nb5O15 is studied particularly in the region x=0.7–0.9 where the crystals remain tetragonal down to at least 77°K. These crystals should have many applications in the quantum electronics field. The temperature and wavelength dependence of the two indices of refraction are reported as well as the temperature dependence of the linear electro‐optic constant and the nonlinear optical effect (second‐harmonic generation). These quantities are discussed in terms of a model that treats these ferroelectrics as biased paraelectrics, the biasing field being supplied by the spontaneous polarization. The agreement is fairly good. To demonstrate the usefulness of these materials an x=0.8 crystal was used for the efficient intracavity harmonic generation of 0.53‐μ light using a 1.06 μ Nd–YAG laser. The same crystal was used to phase lock the laser, thus increasing the harmonic power.

Molten solution grown potassium sodium barium niobate crystals with a tungsten bronze-type structure

Large crystals of the NaBa2Nb5O15-type with K substitututions for Na have been grown in unseeded molten solutions fluxed with excess alkali carbonates. Curie temperatures and phase match temperatures of these crystals are decreased by the substitution of K for Na. Crystal compositions lie in the ternary NaNbO31bKNbO31bBaNb2O6 system and are proportionately BaNb2O6-rich as is the case for crystals pulled from nominally stoichiometric melts. The crystals exhibit 50 to 100 μ regions which are optically uniform.