Versatile flux system grows large, well-formed, stoichiometric single crystals of mixed oxides of the transition-metal elements. These crystals have important uses in the microwave field, and applications as lasers and masers in communications

Arnott, R. J.

Feretti, A.

Kunnamann, W.

English

NASA Technical Reports Server

November 1969	 Brief 69-10642 
•//VCo\ AEC-NASA TECH BRIEF 
TES
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Electrolytic Separation of Crystals of Transition-Metal Oxides 
.
The problem: 
To develop a method of growing crystals of the 
transition-metal oxides, which have important uses in 
the microwave (radar) field, and applications as lasers 
and masers in communications. The growth of large 
crystals is difficult because the melting points of many 
of these mixtures are higher than the dissociation 
temperature of the oxides at atmospheric pressure. 
The chromite series of compounds, while usually quite 
stable, have extremely high melting points (^!: 2000'C); 
they present the problem of finding a container that is 
both inert and resistant to such temperatures. 
The solution: 
An extremely versatile flux system has been devel-
oped for growing large, well-formed, stoichiometric 
single crystals of mixed oxides of the transition-metal 
elements. Single crystals of M' 'Cr2 O4 and M' 'Fe204 
(where M + + is a transition or alkaline-earth ion) and 
the garnet Y 3 Fe5 0 12 have been grown from the 
sodium tungstate-pyrotungstate flux system (l-x) 
Na 2 W 2 07-.xNa 2 WO4 , where I ^: x ^ 0. In addi-
tion, single crystals of the system Co i + 5V 2 _ 504 
(where I ^.x 0)-have been prepared by elecfrolysis 
Of COO—V205 mixtures dissolved in a suitable sodium 
polytungstate flux. 
The phase boundaries present in the CoCr204-. 
Na 2 W 2 07—Na 2 WO 4 system are determined, and 
generally discussed is a solution process for transition-
metal oxides in a sodium pyrotungstate flux formulated 
on Lewis acid-base theory. 
How it's done: 
Fundamentally the polytungstate-flux system can be 
described in terms of Lewis acid-base theory. The 
basic oxides are dissolved by a strong Lewis acid
(W0 3 ) and then reprecipitated by a strong Lewis base 
(Na 2 WO 4 ). This process of solution and reprecipi-
tation can be expressed by the equilibrium equation 
Na 2 W 20 7 (I)	 Na2WO4 (1) + W0 3 (1). 
Sodium pyrotungstate (Na2 W 207 ) is a relatively 
stable compound at low temperatures, dissociating 
only slightly into the acid-base components. As the 
temperature increases, the equilibrium is shifted 
rapidly toward the right. Consequently, at higher 
temperatures, more acid is produced to dissolve the 
transition-metal oxides as complex tungstates, the 
process reversing as the temperature decreases. 
Therefore the only requirements for solubility of a 
particular transition-metal oxide (or mixture of oxides) 
at a temperature T are that (I) a complex tungstate, 
of the transition-metal oxide, must exist at T that is at 
least partially soluble in the flux system; and (2) it 
must be possible to establish at T an equilibrium 
reaction by which the complex tungstate is formed 
through reaction of the metal oxide with a finite 
amount of sodium pyrotungstate. 
The solubility requirements imply the existence of 
an equilibrium reaction at T of the type 
aMeO(s) + bNa 2 W 207 (/)	 aMe0.nW03(s,/)
+ (b-na)Na2 W 207 (/) + NaNa2WO4(/) 
where Me0.nW0 3 (s,/) is a partially soluble complex 
tungstate of a transition-metal oxide MeO. Thus, if a 
moles of a transition-metal oxide are added to the flux 
composition at T, there exists a value of x(x) above 
which the only solid phase that may exist in equilib-
rium with the solution is the transition-metal oxide. 
The value of x is expected to increase as the relative 
basicity of the oxides increases and to be largest for 
alkali and alkaline-earth oxides. 
(continued overleaf) 
This document was prepared under the sponsorship of the Atomic liability resulting from the use of the information contained in this 
Energy Commission and/or the National Aeronautics and Space document, or warrants that the use of any information, apparatus, 
Administration. Neither the United States Government nor any per- method, or process disclosed in this document may not infringe pri-
son acting on behalf of the United States Government assumes any vately owned rights.
Ask
https://ntrs.nasa.gov/search.jsp?R=19690000585 2020-03-16T18:29:54+00:00Z
If a flux composition is chosen for which x = x + Ax 
at temperature T, the amount of solid oxide in equilib-
rium with the solution will decrease as the temperature 
is raised to T + AT. This dissolved oxide may then be 
reprecipitated at any desired rate on subsequent 
cooling. Slow rates of cooling are desirable for growth 
of large single crystals. 
Notes: 
1. This information may interest the electronics and 
communications industries. 
2. U.S. Patent No. 3 382 161 covers this innovation 
3. Inquiries concerning this innovation may be di-
rected to:
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B69-10642 
0
Source: W. Kunnamann, A. Feretti, R. J. Arnott of

Brookhaven National Laboratory

under contract to

Argonne National Laboratory

(ARG- 10506) 
Patent status: 
Inquiries concerning rights for commercial use of 
this innovation may be addressed to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439
S 
S 
Brief 69-10642	 Category 03


Electrolytic separation of crystals of transition-metal oxides

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server